Ever feel hangry when you miss a meal? Imagine waiting 16 or 18 hours before eating again. Or an entire day without breakfast, lunch, or dinner. That’s what proponents of intermittent fasting do on a regular basis.
At its simplest, intermittent fasting (IF) means cycling through periods of voluntary abstinence of food (or significant calorie reduction), interspersed with intervals of normal food intake.
Whenever we eat, the body releases insulin to help cells convert sugars (in particular glucose) from food into energy. If the glucose isn’t used immediately, insulin helps makes sure the excess is stored in fat cells. But when we go without food for extended periods, as people do in IF, insulin is not released. The body then turns to breaking down fat cells for energy, leading to weight loss.
“That’s why we have fat stores, and if we’re not using them, all kinds of bad things happen.”
Monique Tello, MD, MPH, a Harvard Medical School professor and internal medicine physician at Massachusetts General Hospital, explains to Inverse what happens when people never get hungry enough to use up those fat stores. “A, we get fatter, and B, it’s all the things that go along with that,” she says.
“Your blood sugars are constantly high. Your insulin levels are constantly high. You get type 2 diabetes, which is a huge epidemic. Those high blood sugars cause damage to the insides of our arteries. The kidneys are getting clogged up. People go into dialysis. It’s a disaster, basically.”
A century of IF research in humans and animals illustrates her claims. Studies show IF can lead to weight loss, stabilized blood sugar, reduced inflammation, improvements in memory and stress resistance, slowed aging, and longer lifespan — all promising health benefits in return for considerable lifestyle changes.
- What Is Intermittent Fasting?
- What Happens During Intermittent Fasting?
- How to Get Started
- Can You Lose Weight With Intermittent Fasting?
- How to Eat Healthy While Intermittent Fasting
- Will Intermittent Fasting Make You Live Longer?
- What Are the Risks of Intermittent Fasting?
- The Future of Fasting
Intermittent Fasting: Is it Right for You?
- Intermittent Fasting FAQ
- How exactly does intermittent fasting work?
- Is it a difficult diet to follow?
- What is the most effective fasting time window?
- How many days a week is this fasting recommended?
- How much can I eat during the eating period?
- Are there certain beverages that should be consumed during the fasting period?
- Besides weight loss, are there other benefits to intermittent fasting?
- Does it involve counting calories?
- Who benefits most from intermittent fasting?
- Are there certain medical conditions where intermittent fasting should be avoided?
- Intermittent Fasting FAQ
- 12 Possible Health Benefits of Intermittent Fasting
- 1. Weight Loss
- 2. Reduced Blood Pressure
- 3. Reduced Inflammation
- 4. Lower Cholesterol
- 5. Better Outcomes for Stroke Survivors
- 6. Boosted Brain Function
- 7. Cancer Protection
- 8. Increased Cell Turnover
- 9. Reduced Insulin Resistance
- 10. Lower Risk of Cardiovascular Issues
- 11. Increased Longevity
- 12. A Better Night’s Sleep
- Is Your Period Healthy?
- Intermittent Fasting for women: Important information you need to know.
- Intermittent fasting and your health
- Fasting and female hormones
- Why does IF affect women’s hormones more than men’s?
- Putting it all together: The study
- Fertility, meet metabolism
- But, why!?!?!?
- How does the body “know”?
- Stressors and energy balance
- What to do now
- Fasting is not for everyone
- What to do if fasting isn’t for you
- Passionate about nutrition and health?
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- Everything women need to know about intermittent fasting
- 1. What Is Intermittent Fasting?
- 2. What Makes Intermittent Fasting More Complicated For Women?
- 3. How women can safely enjoy the benefits of intermittent fasting while bypassing the risks.
- We Recommend Women To Follow These Simple Rules While Intermittent Fasting:
- 1. Do not fast on consecutive days (fast for instance on Tuesday, Thursday, Saturday)2. Do not fast for more than 12-16 hours (fast for instance from 8pm-10am). Going without food for a longer time may trigger a negative hormonal cascade. In some cases, 14 hours is really the maximum.3. Do not do intensive training on fasting days but rather yoga or light cardio.4. Do not fast right before or during your period.5. Support your body with the best nutrition for your hormonal health. Our Female Cycle Superpowers Program is an amazing program to start with hormone balancing recipes and learn how to best support yourself during different phases in your cycle.
- How I got my period back after throwing my hormones out of whack with intermittent fasting!
- My essential oil bedtime ritual to support a healthy, regular period:
- A guide to 16:8 intermittent fasting
- What is intermittent fasting?
- Does intermittent fasting work for weight loss?
- Is intermittent fasting safe long term?
- Is intermittent fasting good for you?
- How do you start intermittent fasting?
- The three most popular types of intermittent fasting are 16:8, 5:2, and alternate-day fasting.
- Intermittent fasting may help with weight management, but isn’t a guarantee.
- Intermittent fasting benefits for hormones and metabolism are promising, but inconclusive.
- Although IF might be OK for some people, it’s definitely not for everybody.
- Fasting: Health benefits and risks
- The potential benefits of intermittent fasting
- The health risks of fasting
- Could we reap the benefits of fasting without fasting?
- Is intermittent fasting for you? Dr. Oz explains the pros and cons
- What the science shows:
- Benefits of intermittent fasting revealed in new study
- How to adopt intermittent fasting in your life:
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- Is fasting an effective weight-loss method?
- What is Intermittent Fasting and Why Would You Do It?
- How Does Intermittent Fasting Work?
- The Benefits of Intermittent Fasting
- Examples of Different Intermittent Fasting Schedules
- Frequently Asked Questions, Concerns, and Complaints
- 1. You might feel way hungrier.
- 2. It might make you feel sick or fatigued in the morning, especially if you work out first thing.
- 3. Fasting diets are rigid and rule-based.
- 4. It doesn’t always play nice with other diets.
- 5. You may deal with low blood sugar.
- 6. The research is minimal.
- 7. It doesn’t help you create mindful eating habits.
- 8. You can take it too far.
- Ultimately, if you’re just not sure how to feel about intermittent fasting, don’t hesitate to hash it out with a pro, like an RD or doc you trust.
What Is Intermittent Fasting?
Unlike some complicated nutritional plans, IF requires minimal effort: You simply don’t eat, or eat very limited quantities, for hours at a time. No meal prep, counting calories, or restaurant guesswork.
But there are several ways to go about the diet. Some IF proponents maintain time-restricted eating, squeezing all their meals into an eight to 10-hour period, followed by a 14- to 16-hour overnight fast. Others rave about the 5:2 diet, which involves eating normally for five days of the week followed by two days of eating 25% of their daily caloric intake (that’s around 500 to 600 calories for most people). Others simply restrict food intake completely on certain days of the week, relying on water, black coffee, and tea to stave off hunger cues.
There are no guidelines or nutritional suggestions for “on days” when eating is unrestricted. But physicians and dieticians suggest eating a nutrient-dense diet full of plants and protein to tide you over through fasting periods.
Health professionals emphasize maintaining a healthy, balanced diet if intermittent fasting.Unsplash / Jordan Christian
What Happens During Intermittent Fasting?
To understand IF, you have to first understand what happens when you eat.
“Insulin is a hormone that’s released when we eat, but it isn’t meant to be released all the time,” Tello says. “Intermittent fasting is simply letting your insulin level go down to basically normal so that you unlock your fat stores. So nobody’s going to lose any weight unless they get that insulin level down. Which is why eating very small meals throughout the day doesn’t really help with weight loss.”
“People did not have KIND bars.”
Waiting a bit longer than usual between meals is totally normal, she says, despite what societal cues tell us.
“Historically, we didn’t have access to things like snacks even up until a hundred years ago,” Tello says. “People did not have KIND bars. People, nowadays, keep food in their glove compartments, for God’s sake. It’s like people can’t stand to be even a little bit hungry for a second. That’s not normal, that’s not healthy.”
Mark Mattson, Ph.D., a professor of neuroscience at the Johns Hopkins University School of Medicine and former chief of the Laboratory of Neurosciences at the National Institute on Aging, compares how fasting affects the body to the way exercise does.
“During exercise, there’s a stress on the cells. They don’t grow and get stronger and bigger during the exercise but during the resting period. So we think that with intermittent fasting — during the fasting period, the cells go in kind of a stress-resistance mode. And then when you eat, they’ve prepared themselves to quickly take up nutrients, proteins, and grow.”
How to Get Started
When first trying IF, the transition can be challenging, Mattson admits.
Many fasters report uncomfortable, even painful hunger pangs as they abstain from food. Mattson suggests people take it slow, trying different kinds of IF to see what works with their goals and routine. He advises first narrowing the “feeding window” from an initial unrestricted period down to 12 hours, then 10 hours, then eight hours, before finding a feeding window that is sustainable.
During the first week or two of IF, fasters may notice their stomachs grumbling or feel a sense of hollowness. Some people are exhausted, lightheaded, or shaky from diminished blood sugar on fasting days. Others experience poor concentration, irritability, mood swings, and even dizziness. In particular, people who work in long shifts or with heavy machinery should take more care when fasting to stay hydrated, rested, and alert.
After about a month, people typically feel better and less hungry, says Mattson.
Tello agrees: “The longer you can go between meals, the less hungry you are. I think a lot of people’s hunger levels actually decrease as opposed to the very low calorie diet where you’re constantly feeding yourself small, tiny bits of food. That’s like a tease all day long.”
Mattson encourages fasters to be patient and wait for those side effects to pass.
“A lot of people will say, ‘Well, I tried it. I’m too hungry, I’m irritable, and cannot concentrate,’ but they have to stick with it,” he says. “It is kind of like exercise. If you’ve been out of shape, when you start, it takes a while for your body and brain to adjust. But after you get used to it, you actually feel better. And if you stop doing it, you feel worse.”
To make fasting manageable, Tello suggests an overnight fast, which can more easily fit into people’s routines. Research shows that restricting eating to daytime hours, an approach that aligns eating patterns with circadian rhythms, has been shown to have metabolic and weight loss benefits.
“Nighttime eating is horrible,” Tello explains. “Nighttime snacking is like the worst. Eating at night and then going to bed, that all goes right to fat. That is the surest way to gain weight, and it’s so bad for your blood sugars.”
Can You Lose Weight With Intermittent Fasting?
A major reason many people start and stick to IF is to lose weight. A Reddit group centered on the practice, with over 380,000 members, brims with dramatic before and after photos of fasters, some who have dropped over 150 pounds using the weight loss approach. Most rave about their results: slimmer bodies, more energy, and happier outlooks.
A 2015 systematic review of 40 studies, published in Molecular and Cellular Endocrinology, showed that IF was effective for weight loss, with a typical loss of seven to 11 pounds over 10 weeks.
But IF isn’t necessarily more effective for weight loss than other energy restriction regimens, like simply counting calories or cutting out carbs. A year-long study of obese males, published in JAMA Internal Medicine in 2017, showed that alternate-day fasting did not produce superior adherence, weight loss, weight maintenance, or cardioprotection over daily calorie restriction.
The Mediterranean diet includes lots of olive oil, vegetables, fruit, and some fish.Unsplash / Louis Hansel
How to Eat Healthy While Intermittent Fasting
If losing weight in a healthy way is the goal, Tello suggests maintaining a plant-based diet alongside fasting and not using IF as an excuse to overeat or consume unhealthy foods during non-fasting windows. In a plant-based diet, plants make up the lion’s share of food consumption. Think vegetarian, vegan, or Mediterranean diets.
“People do not have to be completely vegan but they do have to be, for the most part, eating plants.”
“We have so much evidence, overwhelming mountains of evidence on millions and millions and millions of people’s data that a plant-based diet is the healthiest diet,” Tello says. “And people do not have to be completely vegan, but they do have to be, for the most part, eating plants.”
Tello suggests aiming to make plants 80% of your diet. You can still have steak, cake, and whole grains on occasion, but the bulk of your diet should be coming from the ground or growing in a tree or bush.
“You will be a healthier person. It’s anti-inflammatory, it’s fiber full. It’s going to be decreasing your cholesterol levels. Your digestion is going to improve,” Tello says.
Decades of research, show that a plant-based diet is effective for controlling or losing weight, improved physical and emotional health, and a multitude of health benefits: lower mortality, better cardiovascular health, prevention of type 2 diabetes, and lower blood pressure and cholesterol.
Will Intermittent Fasting Make You Live Longer?
In 2012, the BBC broadcast journalist Michael Mosley brought IF into the diet landscape with the documentary Eat Fast, Live Longer, which drew on research by Michelle Harvie, Ph.D., at the University of Manchester. It was followed shortly by journalist Kate Harrison’s book The 5:2 Diet in 2013 and Dr. Jason Fung’s The Obesity Code in 2016.
Research on IF’s effects on aging date back a century. “Nutrition and aging are very tightly linked,” John Newman, MD, Ph.D., a geriatrician at the University of California, San Francisco and researcher with the Buck Institute for Research on Aging, tells Inverse.
“One of the great early experiments almost a hundred years ago showed that if you feed rats less food, they live longer up until the point when you start to starve them. Fasting, dietary restriction, and the ketogenic diet turn on repair pathways and help animals to live longer.”
A century of laboratory research on animals and humans, collated by Harvie and Anthony Howell, Ph.D., both at the University of Manchester, links calorie restriction with the prevention of age-related disease, which includes tumors, cardiovascular disease, diabetes, and dementia. The research also suggests that it increases lifespan.
What Are the Risks of Intermittent Fasting?
Some dieticians warn that ignoring hunger cues can have unforeseen consequences. Evelyn Tribole, registered dietitian and author of The Intuitive Eating Workbook, encourages her clients to listen to their hunger and satiety cues when choosing to eat rather than adhering to strict dietary rules. Tribole thinks ignoring these primal signals is a dangerous practice.
“I have a problem when someone is actually feeling biological hunger and you’re going to disregard that,” Tribole says. “I think that’s problematic, especially with anyone who has a dieting history or an eating disorder; they’re more likely to get engaged in binge eating and emotional eating.”
Anyone with a history of disordered eating patterns should consult a health professional to confirm that IF is right for them.
One systematic review published in the journal Stress in 2016, found that IF may initially increase stress levels of fasters. The increase may subside after a few weeks of fasting. Other research says IF could cause greater metabolic fluctuations and increased appetite on non-fasting days relative to intermittent energy restriction, a diet that allows some food.
The Future of Fasting
Mattson, Tello, and Newman note that the research on IF has its limitations. Notably, a bulk of the studies have been done on rats and animal models, or obese or overweight human subjects.
IF’s impact on other populations — like growing adolescents, pregnant women, diabetic people, those with existing medical conditions, people using medication that requires food intake, or people over 65 years of age — remains to be determined.
More randomized controlled studies on a wider range of adult populations would help confirm some of the potential health benefits. But for now, it appears IF is here to stay.
“Intermittent fasting is well beyond a fad,” says Mattson, who is critical of its trendiness because he worries it can lead people to discredit the value of reputable evidence.
“Luckily, there’s plenty of research in human beings and intermittent fasting,” Tello says. “There are all these different studies calling it different words, but they are looking at the same thing, which is extended fasting.”
“At this point,” she concludes, “I think it’s really fair to say that any kind of modified fasting regimen promotes weight loss and improves metabolic health. I think we’re really safe to say that.”
Intermittent Fasting: Is it Right for You?
Weight loss can be difficult, but could intermittent fasting help? This eating pattern, which features cycles of fasting and eating, is making headlines as research confirms it’s not only what you eat, but when you eat, that matters in the struggle to lose weight.
During intermittent fasting, individuals use specific periods of eating — typically within an eight-to-10 hour window — to lose weight, says Michigan Medicine dietitian Sue Ryskamp, who sees patients at U-M’s Frankel Cardiovascular Center.
The premise behind intermittent fasting is relatively simple, she says: “When our insulin levels go down far enough and for long enough, as they do during a fasting period, we’re able burn off fat.”
Insulin levels drop when a person is not consuming food. During a period of fasting, decreasing insulin levels cause cells to release stored glucose as energy. Repeating this process regularly, as with intermittent fasting, leads to weight loss. “In addition, this type of fasting often results in the consumption of fewer calories overall, which contributes to weight loss,” Ryskamp says.
Intermittent fasting also allows the GI tract to rest and repair while in a state of fasting. “This is when your body is able to use fat stored in your cells as fuel, so you’re burning fat instead of storing it, which leads to weight loss,” says Ryskamp. “The results of recent studies look promising, especially when combined with exercise and a plant-based diet such as the Mediterranean diet.”
A Harvard research study also reveals how intermittent fasting may slow the aging process through weight loss, lower blood pressure and reduced cholesterol.
So, is intermittent fasting actually healthy? Are there benefits? Pitfalls? Before deciding if it’s right for you, read Ryskamp’s Q&A below to get all your need-to-know questions answered.
Intermittent Fasting FAQ
How exactly does intermittent fasting work?
The diet works best when you stop eating at a certain time of the day and avoid eating at night altogether. That means no in-between or before-bed snacks. Although the time of eating will differ from person to person, many of my patients find success when they are eating between 10a.m. and 6p.m.
Is it a difficult diet to follow?
Intermittent fasting can be difficult, but as your body adjusts to a new way of consuming foods, the diet gets easier. The overall idea is to be more aware of what and when you’re eating. It gives you limits and boundaries that many of my patients find helpful.
Along with intermittent fasting, we promote daily exercise, avoiding sugars, and choosing fruits, vegetables, beans, lentils, whole grains, lean proteins and healthy fats.
What is the most effective fasting time window?
Fat burning typically begins after approximately 12 hours of fasting and escalates between 16 and 24 hours of fasting.
How many days a week is this fasting recommended?
Typically, people fast for up to 16 hours each day. This is usually done by skipping breakfast in the morning after eating the final meal of the day on the previous day. There is also a pattern of intermittent fasting that involves going 24 hours without food up to two times per week.
How much can I eat during the eating period?
If your goal is to lose weight, aim for a calorie level that supports a weight loss of one to two pounds per week. On average, to lose one pound per week, you’ll need to cut out 500 calories a day.
Are there certain beverages that should be consumed during the fasting period?
Water … and plenty of it. If you plan to engage in fasting, be sure to get lots of fluids in during the hours you’re not eating solid food. Vegetable, chicken or bone broth can also be consumed. Soda and beverages containing caffeine should be avoided.
Besides weight loss, are there other benefits to intermittent fasting?
In addition to reduced body weight, this fasting can help lower cholesterol, improve glucose control, reduce liver fat and improve blood pressure. Patients tell me they have increased endurance, better motor coordination and improved sleep. Eating according to your circadian rhythm (eat day/sleep night) helps promote deep sleep. Studies have also shown that fasting, which leads to caloric restriction, increases the lifespan of even healthy people. Studies also suggest that fasting may reduce tumor growth and could help prevent recurrences of breast cancer.
Does it involve counting calories?
Not necessarily, but if you’re cutting out snacks before bed and going for longer periods of time without eating, your calorie count will decline. Also, when you follow a mostly plant-based diet, you’re consuming foods that are naturally lower in calories.
Who benefits most from intermittent fasting?
Intermittent fasting isn’t for everyone. For individuals who’ve struggled to lose weight, this is another tool to have in their toolkit. In the end, it’s about a person’s lifestyle and the choices they make. They have to weigh the options and decide, “What’s going to work for me?”
Are there certain medical conditions where intermittent fasting should be avoided?
People who are brittle diabetic, those with a history of eating disorders like anorexia and bulimia and pregnant or breastfeeding women should not attempt fasting unless under they are under close supervision of a doctor.
12 Possible Health Benefits of Intermittent Fasting
Intermittent fasting (IF), one of the most talked-about diets right now, is a way of eating that designates periods of time for eating and for fasting. And no signs suggest interest is waning. “IF, in its different forms, is holding a steady pace,” says Kimberley Rose-Francis, RDN, CDE, a nutritionist based in Sebring, Florida. “Recently, actress Jennifer Aniston was quoted stating that IF has made a ‘big difference’ in her life,” as Us Weekly reports.
There are a few different approaches, but the two most popular are 16:8, which calls for squeezing all the day’s meals into an eight-hour window and fasting for the remaining 16 hours, and 5:2, where five days of the week are spent eating normally and two are spent fasting (usually defined as eating only 500 to 600 calories per day).
Why would someone opt for this way of eating versus a standard diet, such as going low-carb or low-fat? Some say fasting has loads of health benefits. “The research so far proves the benefits of IF to the extent that it is worthwhile as a method to lose weight, manage your blood sugar, and slow down the aging process,” says Sara Gottfried, MD, of Berkeley, California, author of The Hormone Cure, The Hormone Reset Diet, and Brain Body Diet.
But not everyone’s on board. “From my standpoint and the standpoint of a lot of other people, it does tend to fall into the next fad diet category,” says Elizabeth Lowden, MD, a bariatric endocrinologist at the Northwestern Medicine Metabolic Health and Surgical Weight Loss Center at Delnor Hospital in Geneva, Illinois. A lot of the data is conflicted, she says, and many studies done on animals have not yet been repeated in people. “For every study that shows there’s no change, there are some studies that show maybe there is improvement,” she says.
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So rather than take the claims at face value, we decided to dive into them and explore whether 10 touted benefits of IF are legit, or the science doesn’t yet stack up.
1. Weight Loss
Most people start IF to lose weight. And that claim seems to hold up, at least in the short term. According to an article published in August 2015 in the Journal of the Academy of Nutrition and Dietetics, there’s a chance that any version of IF may contribute to weight loss. The researchers looked at data from 13 studies and found that average weight loss ranged from 1.3 percent for a two-week trial to 8 percent for an eight-week trial.
That’s probably welcome news if you’re hoping to fast for weight loss, but the fact that those studies were short term means it’s unclear if IF is sustainable and can help you keep extra pounds off in the long run.
The other catch: The amount of weight lost doesn’t seem to be any more than what you’d expect from another calorie-restricted diet, and depending on how many calories you’re eating each day, you could even end up gaining weight. After all, the diet doesn’t restrict high-calorie foods.
When the diet is done properly, IF can be as effective as normal caloric restriction, Dr. Lowden says. Some people, especially busy people who don’t have time to devote to meal planning, might even find a time-restricted diet easier to follow than something like the keto diet or the paleo diet, she says.
RELATED: ‘Intermittent Fasting Helped Me Lose 48 Pounds — Here’s What I Ate (and When)’
2. Reduced Blood Pressure
IF may help lower high blood pressure in the short term. A study published in June 2018 in Nutrition and Healthy Aging found 16:8 significantly decreased the systolic blood pressure among the 23 study participants. The link has been shown in both animal and human studies, according to a review published in March 2019 in Nutrients. And, an October 2019 study published in the European Journal of Nutrition found IF led to even greater reductions in systolic blood pressure than another diet that didn’t involve defined eating times.
Having a healthy blood pressure is important — unhealthy levels can increase your risk for heart disease, stroke, and kidney disease.
But so far the research shows these blood pressure benefits last only while IF is practiced. Once the diet ended and people returned to eating as normal, researchers found the blood pressure readings returned to their initial levels.
3. Reduced Inflammation
Animal studies have shown that both IF and general calorie restriction can reduce inflammation levels, though clinical trials are few and far between. The authors of a study published in Nutrition Research wanted to know if that link existed among humans, too. The study involved 50 participants who were fasting for Ramadan, the Muslim holiday, which involves fasting from sunrise to sunset, and eating overnight. The study showed that during the fasting period, pro-inflammatory markers were lower than usual, as was blood pressure, body weight, and body fat.
RELATED: What Is an Anti-Inflammatory Diet?
4. Lower Cholesterol
According to a three-week-long study published in Obesity, alternate-day fasting may help lower total cholesterol as well as LDL cholesterol when done in combination with endurance exercise. LDL cholesterol is the “bad” cholesterol that can raise your risk of heart disease or stroke, according to the Centers for Disease Control and Prevention. The Obesity researchers also noted that IF reduced the presence of triglycerides, which are fats found in the blood that can lead to stroke, heart attack, or heart disease, according to the Mayo Clinic. One caveat here: The study was short, so more research is needed to understand whether the effects of IF on cholesterol are long lasting.
5. Better Outcomes for Stroke Survivors
Healthier cholesterol levels and lower blood pressure (two benefits noted above) play a major role in helping reduce your risk of stroke. But that’s not the only possible stroke-related benefit of IF. An article in Experimental and Translational Stroke Medicine found that IF and calorie reduction in general may provide a protective mechanism for the brain. In cases where stroke occurs, it seems eating this way prestroke may ward off brain injury. The researchers say future studies are needed to determine whether following IF post-stroke can aid recovery.
6. Boosted Brain Function
Dr. Gottfried says IF may improve mental acuity and concentration. And there’s some early research to support that idea: A study on rats published in February 2018 in Experimental Biology and Medicine found it may help protect against the decline in memory that comes with age. According to Johns Hopkins Health Review, IF can improve connections in the brain’s hippocampus and also protect against amyloid plaques, which are found in patients with Alzheimer’s. This study was done only in animals, though, so it’s still unclear whether the benefit holds true for humans.
RELATED: 3 Key Nutrients for Better Brainpower
7. Cancer Protection
Some studies have shown that alternate-day fasting may reduce cancer risk by decreasing the development of lymphoma, limiting tumor survival, and slowing the spread of cancer cells, according to a review of studies published in The American Journal of Clinical Nutrition. The studies that showed the cancer benefit were all animal studies, though, and more studies are needed to confirm a benefit for humans and understand the mechanism behind these effects.
8. Increased Cell Turnover
Gottfried says the period of rest involved in intermittent fasting increases autophagy, which is “an important detoxification function in the body to clean out damaged cells.” Put differently, a break from eating and digestion gives the body a chance to heal and get rid of junk inside the cells that can accelerate aging, she says.
A study published in May 2019 in Nutrients found that time-restricted feeding, which the researchers defined as eating between 8 am and 2 pm, increased the expression of the autophagy gene LC3A and the protein MTOR, which regulates cell growth. This study was small, involving only 11 participants for four days. Another study, published in August 2019 in Autophagy, also noted that food restriction is a well-recognized way to increase autophagy, specifically neuronal autophagy, which may offer protective benefits for the brain. There were some limitations with this study as well, though: It was done on mice and not humans.
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9. Reduced Insulin Resistance
Gottfried proposes that intermittent fasting may help stabilize blood sugar levels in people with diabetes because it resets insulin, though more research is needed. The idea is that restricting calories may improve insulin resistance, which is a marker of type 2 diabetes, according to a study published in April 2019 in Nutrients. Fasting, such as the kind of fasting associated with IF, encourages insulin levels to fall, which may play a role in reducing the risk for type 2, the study notes. “I have colleagues at other facilities who have seen positive results especially in improvements in insulin needs for diabetics,” Lowden says.
The aforementioned study published in Nutrition and Healthy Aging investigated this effect in humans, and while a 16:8 approach did result in reductions in insulin resistance, the results were not significantly different from the control group. And again, this study was small.
Registered dietitians advise people with diabetes to approach intermittent fasting with caution. People on certain medications for type 2 diabetes or those on insulin (whether to manage blood sugar for type 2 or type 1 diabetes) may be at a greater risk for low blood sugar, which can be life-threatening. Check with your doctor before trying intermittent fasting if you have any type of diabetes, they advise.
10. Lower Risk of Cardiovascular Issues
Per the aforementioned Nutrients study, when insulin levels fall, so does the risk of dangerous cardiovascular events, such as congestive heart failure, which is important for patients with type 2 diabetes because they are two to four times more likely to die from heart disease than adults without diabetes, according to the American Heart Association.
The Nutrients study noted that while there aren’t human studies to confirm the benefit, observational studies have shown IF may deliver both cardiovascular and metabolic benefits. Lowden suspects that changes to metabolic parameters, such as lower levels of triglycerides and a decrease in blood sugar levels, are the result of losing weight and would be achieved no matter how the weight was lost, whether through IF or a low-carb diet, for example.
RELATED: 10 Popular Low-Carb Diets, and Their Pros and Cons
11. Increased Longevity
There have been a few animal and rodent studies that have shown IF may extend life span, possibly because fasting seems to build resistance to age-related diseases. A review published in Current Obesity Reports in June 2019 noted that while these findings are promising, it’s been hard to replicate them in human studies. Until that happens, it’s best to be skeptical about this potential benefit.
12. A Better Night’s Sleep
If you’ve ever felt like you slipped into a food coma after a big meal, you know that diet can have an impact on wakefulness and sleepiness. Some IF followers report being able to sleep better as a result of following this way of eating. “IF and mealtimes may have an impact on sleep,” Rose-Francis says. Why?
One theory is that IF regulates circadian rhythm, which determines sleep patterns. A regulated circadian rhythm means you’ll fall asleep easily and wake up feeling refreshed, though research to support this theory is limited, according to an article published in December 2018 in Nature and Science of Sleep.
The other theory centers on the fact that having your last meal earlier in the evening means you’ll have digested the food by the time you hit the pillow. According to the National Sleep Foundation, digestion is best done when you’re upright, and going to sleep with a full stomach can lead to bedtime acid reflux or heartburn, which can make it hard to fall asleep.
RELATED: How to Quiet a Racing Mind and Fall Asleep, Tonight
If you pay attention to the health headlines, you’ve probably heard about intermittent fasting. Intermittent fasting has been linked with several important health benefits.
But fasting isn’t the same for men and women. If women try fasting but don’t do it properly, it can cause more harm than good.
Because women’s bodies are biologically built for fertility and reproduction. Extended periods without food tell the body that now isn’t a good time for reproduction.
You might be thinking So what? I don’t want to get pregnant now or maybe ever. But fertility isn’t the only problem. Women need to consider that estrogen and progesterone do more in the body than simply get us pregnant. Estrogen helps us with metabolism, weight loss, mood, anxiety and stress, energy, bone density, and cognitive function, to name just a few.
If you’re a woman, intermittent fasting can disrupt estrogen balance and throw a wrench in all these essential physiological processes. But when you know how to use intermittent fasting in a way that is safe for your unique female biochemistry—that is, when you know how to biohack intermittent fasting to improve hormone health instead of harm it—you can reap some amazing benefits.
Keep reading. I walk you through the benefits, dangers, and how-to of intermittent fasting for women below.
Women’s Hormones and Intermittent Fasting
Intermittent fasting has been associated with numerous health benefits (more on that below), but it is also linked to hormone disruption in women. Here’s a close-up look at the cascade of hormone imbalances that can start with intermittent fasting.
First, intermittent fasting can disrupt estrogen balance. Estrogen imbalance may show up as:
- Low energy
- Poor glucose control
- Weight gain
- Impaired cognitive function
- Decreased bone density
- Poor muscle tone
- Reduced skin and hair health
- Poorer cardiovascular health
A disruption in one hormone system in the body can trigger other hormone imbalances. The other major hormone considerations for women when it comes to intermittent fasting are cortisol, the stress hormone, and thyroid hormone. When cortisol is imbalanced, symptoms include:
- Low energy
- Feeling wired-but-tired
- Sugar cravings
When thyroid hormones are imbalanced, symptoms include:
- Weight gain
- Brain fog
- Dry skin
- Dry hair
- Irregular periods
- Trouble regulating body temperature
So while intermittent fasting may have some benefits, this cascade of negative health effects for women may outweigh any benefit.
What is Intermittent Fasting?
Simply put, it is going for short or intermediate periods of time without food. This “not eating” window can be as short as 12 hours and include sleep time—for example, you could stop eating at 8:00pm one night and not eat again until 8:00am the next morning and call it a fast—or as long as 16, 20, or 24 hours.
People fast in different ways. Some people try to go 12 or more hours without eating everyday. Others try to go 12 or 16 hours without food a couple days a week. Some people don’t eat for a full 24 hours one day each week.
Why Intermittent Fasting is So Hot Right Now
Studies have shown that intermittent fasting may help improve certain health conditions, including:
- Intermittent fasting is associated with improved insulin sensitivity. Insulin sensitivity is an important factor in hormone balance and in overall health
- Intermittent fasting has been linked to reduced body fat
- Meta-analysis also suggests that adherents to intermittent fasting regimens don’t compensate by overeating during their designated eating windows. In fact, studies suggest that there is a “carry over effect” of calorie reduction by as much as 20 percent on eating days
- Intermittent fasting may improve health biomarkers associated with Type 2 diabetes
- Intermittent fasting may improve cognitive function and quiet neuroinflammation in the brain
- Intermittent fasting may help dampen stress hormone production in certain situations
- Intermittent fasting may help lower the risk of chronic health conditions
What Makes Intermittent Fasting Trickier For Women
A woman’s reproductive function is intricately connected to her metabolic function, and vice versa. So anytime a woman’s body gets a “starvation signal” from her environment (like not eating for a stretch of time), it goes into preserve and protect mode, where it holds onto weight (to survive the famine), increases production of the hunger hormones ghrelin and leptin (so that you feel famished and rush to get food ASAP), and slows down non-essential functions like reproduction (so you can keep yourself alive and not waste energy on growing a baby).
Animal studies bear this out: in one study, female rats who engaged in intermittent fasting for 12 weeks had smaller ovaries and experienced more insomnia than male mice. But the researchers found that these changes started in as soon as two weeks after the female mice started intermittent fasting.
How Women Can Use Intermittent Fasting Safely
This doesn’t mean women have to miss out on the benefits of intermittent fasting. Instead, I recommend that women follow some simple rules when it comes to intermittent fasting. This will help you tap into the many benefits associated with intermittent fasting while sidestepping the risks.
- Don’t fast on consecutive days
- Instead, pick no more than two or three non-consecutive days in a week to practice intermittent fasting
- Don’t fast for more than 12 or 13 hours at a time. Going any longer can trigger a negative hormonal cascade
- Don’t do intense workouts on fasting days
- Don’t fast when you’re bleeding
- During your eating window, choose the best diet for your hormonal health
- If you give this slow and steady approach to intermittent fasting a try for a couple months and feel great, you can consider going for a longer window of time each day without eating (up to 16 hours), but pay close attention to how you feel and drop back to a smaller window—or stop intermittent fasting all together—if you start experiencing symptoms of hormone imbalance
If you start to experience symptoms of hormone imbalance while intermittent fasting, or if the hormone imbalance symptoms you already experience get worse, stop fasting right away. These symptoms include:
- Your period becomes irregular or stops
- You start having problems sleeping or falling asleep
- You notice changes in metabolism and digestion
- You feel moody or experience brain fog
- You notice negative changes in how your hair and skin looks
- You’re always cold
Do NOT Try Intermittent Fasting If…
- You have a history of eating disorders
- You’re pregnant or are trying to conceive
- You have trouble falling asleep, staying asleep or trouble waking up in the morning
- You have adrenal fatigue
- You are currently dealing with PMS, PCOS, Fibroids, Endometriosis or other diagnosed hormonal issues
Always remember, that once you have the right information about how your body really works, you can start making health choices that finally start to work for you! You can do this – the science of your body is on your side!
Is Your Period Healthy?
How do you know if your hormones are healthy? The answer is in your 5th vital sign – your period.
The color of your flow, frequency of your period, and symptoms you have each month can tell you a lot about your health. There are 5 different V-SIGN TYPES, and knowing which one you have will help you get healthy now and prevent disease in the future.
Intermittent Fasting for women: Important information you need to know.
Some women who try intermittent fasting experience missed periods, metabolic disturbances, and even early-onset menopause. Sure, it can work for some women. But here’s why intermittent fasting could be bad — even counterproductive — for your goals.
- Want to listen instead of read?
For as long as I can remember, my dad has eaten once a day. Once.
In the morning he gets up and drinks black coffee. That’s it — no eggs, no cereal, no muffin.
Lunch: more nothing.
For supper, he eats a decent-sized meal at home.
The whole thing is even more impressive considering that Dad owns a restaurant!
As a kid, I shrugged it off. Dads do crazy stuff (at least he didn’t play the accordion). He was always in great health, and at 74, he still is today.
My mom couldn’t be more different. She’s at the breakfast table within an hour of waking up, never willingly misses lunch or supper, and if the time between meals gets too long, she fixes herself a snack. She’s the kind of person who keeps almonds in her car just in case she starts to feel peckish while she’s out and about.
I won’t say how old Mom is, but she’s also in great health, and always has been.
Years ago, as I began to immerse myself in a career dedicated to the study of nutrition and sport, I started to wonder:
How can two people who eat so differently be so similarly healthy?
Back then, I had no idea that my father was decades ahead of his time — a kind of pioneer of a now super-buzzworthy diet called intermittent fasting.
Intermittent fasting and your health
Intermittent fasting (IF) is the practice of going for prolonged periods without eating.
There are lots of ways to do it, including meal skipping, alternate-day fasting, Eat Stop Eat, and others (PN’s free e-book on intermittent fasting offers an excellent rundown).
There’s evidence that IF, when done properly, might help regulate blood glucose, control blood lipids, reduce the risk of coronary disease, manage body weight, help us gain (or maintain) lean mass, reduce the risk of cancer, and more.
We even published an article suggesting it could help us live longer and stronger. So, naturally, a lot of people are trying it.
An accompanying trend that’s emerged: While some women who try IF say it’s the best thing that’s happened to them since grapefruit, others report serious problems, including binge eating, metabolic disruption, lost menstrual periods, and early-onset menopause. This has happened in women as young as their mid-20s.
Maybe my mom was on to something. Maybe IF is totally different for women than for men.
Fasting and female hormones
In the grand scheme of your life’s health decisions, experimenting with IF seems tiny, right? Unfortunately — for some women, at least — it seems like small decisions can have big impacts.
It turns out that the hormones regulating key functions like ovulation are incredibly sensitive to your energy intake.
In both men and women, hypothalamic-pituitary-gonadal (HPG) axis — the cooperative functioning of three endocrine glands — acts a bit like an air traffic controller.
- First, the hypothalamus releases gonadotropin releasing hormone (GnRH).
- This tells the pituitary to release luteinizing hormone (LH) and follicular stimulating hormone (FSH).
- LH and FSH then act on the gonads (a.k.a. testes or ovaries).
- In women, this triggers the production of estrogen and progesterone — which we need to release a mature egg (ovulation) and to support a pregnancy.
- In men, this triggers the production of testosterone and sperm production.
Because this chain of reactions happens on a very specific, regular cycle in women, GnRH pulses must be very precisely timed, or everything can get out of whack.
GnRH pulses seem to be very sensitive to environmental factors, and can be thrown off by fasting.
Even short-term fasting (say, three days) alters hormonal pulses in some women.
There’s even some evidence that missing a single regular meal (while of course not constituting an emergency by itself) can start to put us on alert, perking up our antennae so our bodies are ready to quickly respond to the change in energy intake if it continues.
Maybe this is why certain women do just fine with IF while others run into problems.
Why does IF affect women’s hormones more than men’s?
We’re not totally sure.
But it might have something to do with kisspeptin, a protein-like molecule that neurons use to communicate with each other (and get important stuff done).
Kisspeptin stimulates GnRH production in both sexes, and we know that it’s very sensitive to leptin, insulin, and ghrelin — hormones that regulate and react to hunger and satiety.
Interestingly, females mammals have more kisspeptin than males. More kisspeptin neurons may mean greater sensitivity to changes in energy balance.
This may be one reason why fasting more readily causes women’s kisspeptin production to dip, tossing their GnRH off kilter.
Putting it all together: The study
It would be nice to find a human study to illustrate the science I’ve been describing here, but, as I mentioned, there are none. So instead, we’ll look at a recent study on rats:
Intermittent fasting dietary restriction regimen negatively influences reproduction in young rats: A study of hypothalamo-hypophysial-gonadal axis.
The subjects included 10 male and 10 female normal-sized rats.
- Half the rats ate whenever they wanted.
- The other half ate only every second day. In between feeding times, their food was removed and they fasted.
This went on for 12 weeks, which is the equivalent of about 10 years in a human life.
By the end of the 12 weeks, the fasting female rats had lost 19 percent of their body weight, their blood glucose levels were lower, and their ovaries had shrunk.
Overall, the experiment affected the female rats’ hormones much more significantly than the males’.
While kisspeptin production went down in both male and female fasting rats, in the females, LH absolutely plummeted, while estradiol, a hormone that inhibits GnRH in humans, skyrocketed to four times higher than the normal level.
The appetite hormone leptin was six times lower than in a normally fed female rat.
It only took 10-15 days for the experiment to disrupt their reproductive cycle.
In other words, the female rats’ hormones — both reproduction- and appetite-regulating — were totally out of whack.
What does this mean for humans?
It’s hard to say. But based on what we do know about the HPG axis, kisspeptin, the relationship of hormones to appetite, and women’s sensitivity to environmental factors, it’s plausible that fasting could have a similarly dramatic effect in human females.
Fertility, meet metabolism
You might be thinking: So, what’s the big deal if kisspeptin drops off and I miss a few periods? I’m not having kids anytime soon, anyway.
Here’s the thing.
The female reproductive system and metabolism are deeply intertwined. If you’re missing periods, you can bet that a bunch of hormones have been disrupted — not just the ones that help you get pregnant.
Take this snapshot.
In general, women tend to eat less protein than men. Fasting women, obviously, will consume even less.
Consuming less protein means taking in fewer amino acids.
Amino acids are needed to activate estrogen receptors and synthesize insulin-like growth factor (IGF-1) in the liver. IGF-1 triggers the uterine wall lining to thicken and the progression of the reproductive cycle.
Hence, low protein-diets can reduce fertility. (Not to mention sexytime.)
And importantly, estrogen isn’t just for reproduction.
We have estrogen receptors throughout our bodies, including in our brains, GI tract, and bones. Change estrogen balance and you change metabolic function all over: cognition, moods, digestion, recovery, protein turnover, bone formation…
When it comes to appetite and energy balance, estrogen works in a few ways.
First, in the brainstem, estrogens modify the peptides that signal you to feel full (cholecystokinin) or hungry (ghrelin).
In the hypothalamus, estrogens also stimulate neurons that halt production of appetite-regulating peptides.
Do something that causes your estrogen to drop, and you could find yourself feeling a lot hungrier — and eating a lot more — than you would under normal circumstances.
Estrogens are thus key metabolic regulators.
Yes, estrogens, plural. Because the ratios of the estrogenic metabolites (estriol, estradiol, and estrone) change over time. Before menopause, estradiol is the big player. After menopause, it drops, while estrone stays about the same.
The exact roles of each of these estrogens remain unclear. But some theorize that a drop in estradiol may trigger an increase in fat storage. Why? Because fat is used to make estradiol.
This may partly explain why some women find it harder to lose fat after menopause. And it might serve as a reason to care about your reproductive health — even if you’re not focused on making babies.
I know, I know — not fair.
Men get to walk around looking ripped, and you’re struggling to get abs. Well, maybe, evolutionarily speaking, you shouldn’t try so hard to get that washboard stomach if you’re female.
Low-energy diets can reduce fertility in women. Being too lean is a reproductive disadvantage. Female bodies are exquisitely tuned to any threats to energy and fertility.
When you think about it, this makes good evolutionary sense.
Human females are totally unique in the mammalian world. Get this: Nearly all other mammals can terminate or pause a pregnancy pretty much whenever they need to. You’ve known this since middle school health class: Female humans can’t.
In humans, the placenta breaches the maternal blood vessels, and the fetus is in complete control.
The baby can block the action of insulin in order to hoard more glucose for itself. The fetus can even make the mother’s blood vessels dilate, adjusting the blood pressure to get ahold of more nutrients.
That baby is determined to survive no matter what the cost to the mother. This phenomenon, which scientists actually compare to the host-virus relationship, is what’s known as “maternal-fetal conflict.”
Once a woman becomes pregnant, she can’t sweet-talk the fetus to stop growing. The result: Fertility at the wrong time — like, during a famine — could be fatal.
No wonder the reproductive pathway is sensitive to metabolic cues at multiple levels.
How does the body “know”?
OK, so women’s hormonal balance is particularly sensitive to how much, how often, and what we eat.
But how do our bodies “know” when food is scarce?
For many years, scientists believed that it was a woman’s body fat percentage that regulated her reproductive system.
The idea was that if your fat reserve dipped below a certain percentage (somewhere around 11 percent might be a reasonable guess), hormones would get messed up and your period would stop. Boom: no risk of pregnancy.
This makes a lot of sense. If there isn’t much to eat, you’ll lose body fat over time.
But the situation is actually more complicated than that. After all, food availability can change quickly. And — as you probably know if you’ve ever tried to lose weight — body fat often takes a while to drop, even if you’re eating fewer calories.
Meanwhile, women who aren’t especially lean can also stop ovulating and lose their periods.
That’s why scientists have come to suspect that overall energy balance may be more important to this process than body fat percentage per se.
Stressors and energy balance
Specifically, negative energy balance in women may be to blame for the hormonal domino effect we’ve been talking about. And it’s not just about how much food you eat.
Negative energy balance can result from:
- too little food
- poor nutrition
- too much exercise
- too much stress
- illness, infection, chronic inflammation
- too little rest and recovery
Heck, we can even use up energy reserves by trying to keep warm.
Any combination of these stressors could be enough to put you into negative energy balance and stop ovulation: training for a marathon and nursing a flu; too many days in a row at the gym and not enough fruits and vegetables; intermittent fasting and busting your butt to pay the mortgage.
You’re thinking, did she just reference paying the mortgage?
You bet. Psychological stress can absolutely play a role in damaging our hormonal equilibrium.
Our bodies can’t tell the difference between a real threat and something imaginary generated by our thoughts and feelings. (Such as worrying about how you’re going to get abs.)
The stress hormone cortisol inhibits our friend GnRH, and suppresses the ovaries’ production of estrogen and progesterone.
Meanwhile, progesterone is converted to cortisol during stress, so more cortisol means less progesterone. This leads to estrogen dominance in the HPG axis. More problems.
You could be hovering at 30 percent fat. But if your energy balance is negative for a long enough time, especially if you’re stressed, reproduction stops.
That’s the theory, anyway.
What to do now
Based on what we know, intermittent fasting probably affects reproductive health if the body sees it as a significant stressor.
Anything that affects your reproductive health affects your overall health and fitness.
Even if you don’t plan to have kids.
But intermittent fasting protocols vary, with some being much more extreme than others. And factors such as your age, your nutritional status, the length of time you fast, and the other stresses in your life—including exercise—are also likely relevant.
So. Is fasting for you?
Considering how much remains unclear, I would suggest a conservative approach.
If you want to try IF, begin with a gentle protocol, and pay attention to how things are going.
Stop intermittent fasting if:
- your menstrual cycle stops or becomes irregular
- you have problems falling asleep or staying asleep
- your hair falls out
- you start to develop dry skin or acne
- you’re noticing you don’t recover from workouts as easily
- your injuries are slow to heal, or you get every bug going around
- your tolerance to stress decreases
- your moods start swinging
- your heart starts going pitter-patter in a weird way
- your interest in romance fizzles (and your lady parts stop appreciating it when it happens)
- your digestion slows down noticeably
- you always seem to feel cold
Fasting is not for everyone
The truth is, some women should not even bother experimenting. Don’t try IF if:
- you’re pregnant
- you have a history of disordered eating
- you are chronically stressed
- you don’t sleep well
- you’re new to diet and exercise
Pregnant women have extra energy needs. So if you’re starting a family, fasting is not a good idea.
Ditto if you’re under chronic stress or if you aren’t sleeping well. Your body needs nurturing, not additional stress.
And if you’ve struggled with disordered eating in the past, you probably recognize that a fasting protocol could lead you down a path that might create further problems for you.
Why mess with your health? You can achieve similar benefits in other ways.
If you’re new to diet and exercise, IF might look like a magic bullet for weight loss.
But you’d be a lot smarter to address any nutritional deficiencies before you start experimenting with fasts. Ensure you’re starting from a solid nutritional foundation first.
What to do if fasting isn’t for you
How can you get in shape and lose weight if intermittent fasting isn’t a good option for you?
It’s simple, really.
Learn the essentials of good nutrition. It’s by far the best thing you can do for your health and fitness.
Cook and eat whole foods. Exercise regularly. Stay consistent. And if you’d like some help to do all of that, hire a coach.
Sure, intermittent fasting may be popular. And maybe your brother or your boyfriend or your husband or even your dad finds it an excellent aid to fitness and health.
But women are different than men, and our bodies have different needs.
Listen to your body. And do what works best for you.
Passionate about nutrition and health?
If so, and you’d like to learn more about it, consider the Precision Nutrition Level 1 Certification. Our next group kicks off shortly.
What’s it all about?
The Precision Nutrition Level 1 Certification is the world’s most respected nutrition education program. It gives you the knowledge, systems, and tools you need to really understand how food influences a person’s health and fitness. Plus the ability to turn that knowledge into a thriving coaching practice.
Developed over 15 years, and proven with over 100,000 clients and patients, the Level 1 curriculum stands alone as the authority on the science of nutrition and the art of coaching.
Whether you’re already mid-career, or just starting out, the Level 1 Certification is your springboard to a deeper understanding of nutrition, the authority to coach it, and the ability to turn what you know into results.
Interested? Add your name to the presale list. You’ll save up to 30% and secure your spot 24 hours before everyone else.
We’ll be opening up spots in our next Precision Nutrition Level 1 Certification on Wednesday, April 8th, 2020.
If you want to find out more, we’ve set up the following presale list, which gives you two advantages.
- Pay less than everyone else. We like to reward people who are eager to boost their credentials and are ready to commit to getting the education they need. So we’re offering a discount of up to 30% off the general price when you sign up for the presale list.
- Sign up 24 hours before the general public and increase your chances of getting a spot. We only open the certification program twice per year. Due to high demand, spots in the program are limited and have historically sold out in a matter of hours. But when you sign up for the presale list, we’ll give you the opportunity to register a full 24 hours before anyone else.
If you’re ready for a deeper understanding of nutrition, the authority to coach it, and the ability to turn what you know into results… this is your chance to see what the world’s top professional nutrition coaching system can do for you.
Everything women need to know about intermittent fasting
Intermittent fasting (IF) is trending. And we get why! It’s an amazing tool for weight loss, decreasing inflammation, and balancing hormones. But even though we love recommending it to many of our clients – with great results — we also want to share the downsides of intermittent fasting and remind you to keep your female body balanced.
As women our hormone-radars are extremely sensitive to our environment and actions. Intermittent fasting is different for us than it is for men.
That’s why we want to show you how you’ll still be able to tap into the benefits of intermittent fasting – such as improved digestion, metabolism, energy, fat-burning, and better physical performance — while also taking care of your hormonal health without losing your cycle.
1. What Is Intermittent Fasting?
Intermittent fasting is an eating pattern where you cycle between periods of eating and fasting. It does not say ‘what’ foods to eat, but rather ‘when’ to eat them. There are several intermittent fasting methods. The most popular method is 16/8. 16 hours of fasting (including your sleeping hours) and eating your food within a span of 8 hours. No food is allowed during the fasting period, but you can drink water (infused with lemon or essential oils to spice it up) and herbal tea.
2. What Makes Intermittent Fasting More Complicated For Women?
Us women need to support a monthly chain reaction of hormones. Therefore we need to take extra care of avoiding the negative effects intermittent fasting can have on our bodies.
One hormone in particular, the Gonadotropin-releasing hormone (GnRH), is extremely sensitive to environmental factors and can be thrown off by fasting. It’s supposed to trigger the release of FSH & LH, both hormones that influence the ovaries, which are then supposed to activate the production of estrogen and progesterone. Even 3-day fasts have been shown to mess with GnRH pulses which leads to lower estrogen and progesterone production.
But women need estrogen! There are estrogen receptors everywhere in our bodies! Estrogen helps us with metabolize, lose weight, stabilize mood, anxiety, and stress, boost energy, tone muscles, repair skin, and hair, improve bone density, and is even important for cognitive function!
Same for progesterone! In a stress situation (such as a long period of fasting) your body will always prioritize the production of stress hormones such as cortisol and adrenalin over progesterone. Progesterone impacts important physiological processes such as your monthly ovulation and menstruation, as well as sleep and stress response. Too little progesterone leads to water retention, anxiety, low energy, insomnia, sugar addiction, mood swings, weight gain, and PMS. The opposite of what women want when they embark on their intermittent fasting journey!
3. How women can safely enjoy the benefits of intermittent fasting while bypassing the risks.
First of all, everyone reacts differently to intermittent fasting. Some may just experience the benefits while others start experiencing absent periods and water retention.
That’s why it’s so important to listen to your body. Just because someone said it’s supposed to be a certain way or because „everyone is doing it“ doesn’t mean it’s the right thing for you! Embrace your uniqueness.
We Recommend Women To Follow These Simple Rules While Intermittent Fasting:
1. Do not fast on consecutive days (fast for instance on Tuesday, Thursday, Saturday)
2. Do not fast for more than 12-16 hours (fast for instance from 8pm-10am). Going without food for a longer time may trigger a negative hormonal cascade. In some cases, 14 hours is really the maximum.
3. Do not do intensive training on fasting days but rather yoga or light cardio.
4. Do not fast right before or during your period.
5. Support your body with the best nutrition for your hormonal health. Our Female Cycle Superpowers Program is an amazing program to start with hormone balancing recipes and learn how to best support yourself during different phases in your cycle.
How I got my period back after throwing my hormones out of whack with intermittent fasting!
I lost my period and messed up my hormones with too intense intermittent fasting, an overactive lifestyle and stress. But the good news is that I naturally found my way back to hormone balance and regained a regular cycle, symptom-free period, more energy, organized mind and self-love!
And here is how I did that…
Reduce Your Fasting Periods
During the first two weeks of my cycle (follicular & ovulation phases) I really listen to my body and match the fasting to my daily activity level. When I’m really active I reduce the fasting hours from 16 to 12 hours. And sometimes a late-night dinner with friends is what your soul needs, right?
During the last two weeks of my cycle (the week before and during my period — luteal and menstrual phases) I stop intermittent fasting completely and also take it easy on my fitness routine (rather walking, yoga, hiking, and biking).
This supports a healthy hormone production by reducing the stress on your body. It helps to promote the right ratio of progesterone and estrogen for your ovulation and menstruation over the course of your monthly cycle.
Nourish Your Temple With Hormone Balancing Foods
I decided to do our Female Cycle Superpowers Program again, to support my body with hormone balancing foods, mindfulness and lifestyle decisions. Everything is connected and this program is perfect to get a deeper understanding of your hormone situation in every phase of your cycle. And you no longer need to get lost wasting time on the Internet trying to find solutions that may or may not work.
Besides teaching me what foods to eat for optimal hormonal health, the program’s workbooks help me connect with myself, step into my full power, and feel back in control of my health, mood and feelings. This is important for me, because we get so easily lost, disconnected and numb in the busy-ness of our society.
The Female Cycle Superpowers Program shows me to embrace the beauty of my sensitivity again, taking the signs of my body serious and most importantly realizing how powerful and amazing the right food choices actually are. Including their effect on your mental and physical health (which is such a freeing feeling once you’ve lost the control over it). I tell you: Never underestimate of tapping into the power of your own nature — it’s the ultimate energy update throughout all areas of your life!
Extra Boost Of Plant Medicine
Last but not least I also gave my body an extra dose of goodness with the purest plant extracts on earth. I created an extra essential oil routine for the last two weeks of my cycle. This supports my hormone production and cell health and provides my body with a calming effect.
That way it has more energy left for optimal ovulation and menstruation processes, as well as your other hormone functions including sleep, metabolism, detoxification, digestion, regeneration, and immunity.
My essential oil bedtime ritual to support a healthy, regular period:
This essential oil has extensive scientific research to back up its health benefits. Most importantly, it’s an effective tool in reducing cortisol — the stress hormone that can set of a cascade of hormonal imbalances. It also to provides better sleep, relaxation and stress relief.
I diffuse 2-3 drops for 1-2 hours before I go to bed or while falling asleep.
Clary Calm – Monthly Blend for Women
This essential oil blend contains Clary Sage, Lavender, Bergamot, Roman Chamomile, Cedarwood, Ylang Ylang, Geranium, Fennel, Carrot Seed, Palmarosa, and Vitex. The oils each provide a calming, soothing effect to help balance your hormones.
It helps regulate estrogen levels to promote the right ratio of estrogen and progesterone you need for a regular and symptom-free period. Bye-bye cramps, water retention, and headaches! This blend also helps relieve mood swings and emotional rollercoasters during the premenstrual and menstrual time.
Simply apply on your abdomen, neck and pulse points, with the roller bottle it comes in, to experience a soothing, calming and relieving effect.
This essential oil reduces high stress levels and supports your immune system with an extra antioxidant boost. It might even help balance progesterone levels in your body by improving progesterone production.
Anecdotal research discussed in the Proceedings of the Society of Experimental Biology and Medicine noted that of 150 herbs tested for progesterone production that inhibit the growth of human breast cancer cells. Thyme is one of the top six herbs to have the highest estradiol and progesterone binding properties. However, further research is needed.
I put 2-3 drops under my feet before going to bed and sometimes in the morning. You can also use it topically for better skin mixed with a carrier oil like almond or coconut oil.
Here’s how to get the best essential oils at wholesale price (meaning you’ll get -25% off!), including a private 1:1 wellness consultation!
Always make sure to use the highest quality of essential oils, and that they’re certified pure & therapeutic grade. This means your product actually contains the constituents that have these beneficial effects and is safe to use on your body! Learn more about this topic and how to start your healthy oil journey here.
If you experience irregular or missing periods, intermittent fasting is only one of the possible reasons. It’s important to find out your individual root-cause to get your period back on track: We’re here to help! You’re kindly invited to book a free 1:1 coaching call with us here.
Now, beautiful fellow go-getters, I would love to hear from you in the comments below!
What are your experiences with intermittent fasting? What you’ve got to say may help and inspire others to embrace self-care too!
Also, when you know someone who needs to hear about the effects of intermittent fasting and how to reverse it – forward this to them right away.
We’re so grateful to have you here with us!
Healthy, Happy Vibes! x
A guide to 16:8 intermittent fasting
Researchers have been studying intermittent fasting for decades.
Study findings are sometimes contradictory and inconclusive. However, the research on intermittent fasting, including 16:8 fasting, indicates that it may provide the following benefits:
Weight loss and fat loss
Eating during a set period can help people reduce the number of calories that they consume. It may also help boost metabolism.
A 2017 study suggests that intermittent fasting leads to greater weight loss and fat loss in men with obesity than regular calorie restriction.
Research from 2016 reports that men who followed a 16:8 approach for 8 weeks while resistance training showed a decrease in fat mass. The participants maintained their muscle mass throughout.
In contrast, a 2017 study found very little difference in weight loss between participants who practiced intermittent fasting — in the form of alternate-day fasting rather than 16:8 fasting — and those who reduced their overall calorie intake. The dropout rate was also high among those in the intermittent fasting group.
Supporters of intermittent fasting suggest that it can prevent several conditions and diseases, including:
- type 2 diabetes
- heart conditions
- some cancers
- neurodegenerative diseases
However, the research in this area remains limited.
A 2014 review reports that intermittent fasting shows promise as an alternative to traditional calorie restriction for type 2 diabetes risk reduction and weight loss in people who have overweight or obesity.
The researchers caution, however, that more research is necessary before they can reach reliable conclusions.
A 2018 study indicates that in addition to weight loss, an 8-hour eating window may help reduce blood pressure in adults with obesity.
Other studies report that intermittent fasting reduces fasting glucose by 3–6% in those with prediabetes, although it has no effect on healthy individuals. It may also decrease fasting insulin by 11–57% after 3 to 24 weeks of intermittent fasting.
Time-restricted fasting, such as the 16:8 method, may also protect learning and memory and slow down diseases that affect the brain.
A 2017 annual review notes that animal research has indicated that this form of fasting reduces the risk of nonalcoholic fatty liver disease and cancer.
Extended life span
Animal studies suggest that intermittent fasting may help animals live longer. For example, one study found that short-term repeated fasting increased the life span of female mice.
The National Institute on Aging point out that, even after decades of research, scientists still cannot explain why fasting may lengthen life span. As a result, they cannot confirm the long-term safety of this practice.
Human studies in the area are limited, and the potential benefits of intermittent fasting for human longevity are not yet known.
- Intermittent fasting is a popular weight-loss diet among celebs, but so far research hasn’t definitively proved that it produces better results than eating regular meals.
- People who do intermittent fasting will restrict when or how much they can eat in a given period of time, like only eating within an eight-hour window each day.
- If you’re interested in trying intermittent fasting, get the best benefit by cutting out late-night snacking. It’ll help you eat more purposefully and get more sleep.
Intermittent fasting is a hot topic in nutrition and weight loss lately (everyone from Hoda Kotb to Jennifer Aniston has tried it), but the concept itself isn’t new. In fact, temporarily going without eating or drinking stems from the practices of many major world religions and cultures. But intermittent fasting or “IF” — a trend gaining major traction among celebrities (Terry Crews! Jimmy Kimmel! Hugh Jackman!) — does things a bit differently for purported health, weight, and cognitive benefits.
While limiting your meal times can make your eating more purposeful, intermittent fasting is not a fit for everyone. Read on before you decide to start skipping out on snacks.
What is intermittent fasting?
Intermittent fasting generally describes a simple concept: You can eat pretty much whatever you want, but only during a specific period of time. There are few common schedules that IF proponents follow, according to the Journal of the Academy of Nutrition and Dietetics:
Time-restricted fasting: This schedule, which includes the popular 16:8 method, has you fasting for about 16 hours per day and eating within an eight-hour window. Most people do this by starting their fast at night, skipping breakfast, and eating their first meal around lunchtime. That gives them another seven or so hours to feed themselves until tomorrow.
Modified fasting: This option, commonly known as the 5:2 diet, allows you to eat about 25% of your recommended calorie needs on two fasting days each week and eat without restriction on the other five days.
Alternate fasting: In this less regimented style, you switch between periods of consuming zero-calorie beverages and actual eating. Some fans follow a high-fat or ketogenic diet on their days off from fasting. The fasts can end after less than 12 hours, while others can stretch as long as a full week! The Eat-Stop-Eat method, for example, calls for a 24-hour fast once or twice a week.
Does intermittent fasting work for weight loss?
Currently, there are a few claims but not much by the way of science in favor of long-term fasting for health or weight loss. Alternate-day fasting did not help people lose more weight or keep weight off longer than people who simply restricted daily calories, according to a 2017 study published in the Journal of the American Medical Association.
The other bad news for fasting fans? LDL or “bad” cholesterol increased in the alternate fasting day group compared to control groups in a 2016 trial. Other risk indicators stayed the same across groups on this trial and other similar ones.
But a new scholarly review, which examined previously published research on the effects of fasting diets in both humans and animals, suggests that regularly abstaining from food may aid those struggling to manage their weight in the long term. Published in the December 2019 issue of The New England Journal of Medicine, the review suggests that IF could help dieters lower their blood pressure naturally and may even have an impact on lifespan. The authors behind the new research only considered evidence linked to 16:8 time-restricted plans as well as 5:2 intermittent fasting. Like other limited studies conducted on animals, this review suggested that fasting may reduce insulin production and overall sugar uptake in fat cells, which could potentially lower one’s risk of chronic disease.
According to Mark Mattson, Ph.D., a professor of neuroscience at Johns Hopkins University and one of the review’s authors, early research has been limited by the fact that fasting isn’t the norm for most Americans. But new evidence may help health experts explore the benefits of fasting for those who may be struggling to lose weight — as well as those diagnosed with cancer, diabetes, or cardiovascular conditions, according to a new pilot study conducted on humans published in the journal Cell Metabolism in December.
Is intermittent fasting safe long term?
Intermittent fasting plans have the potential to backfire tremendously — especially if your goal is to lose weight. Fasting can lead to nausea, dehydration, and even weight gain over time. There hasn’t been enough definitive research that has effectively looked at the long-term effects of fasting on metabolism. You may also eat more than you thought you would during your days or times of “feasting” too. In his review, Mattson advises that anyone attempting to fast should gradually increase the duration and frequency of their fasts over longer periods of time — and that physicians should closely monitor your progress.
Eating real, nutrient-dense foods on a consistent basis fuels us physically, mentally, and emotionally. So if intermittent fasting works for you, go for it! But if it makes you feel anxious, depressed, or isolated in any way, it may not be the best plan for you personally.
Plus, I’d be remiss to mention who should absolutely not dabble in this eating style: Anyone who’s previously struggled with an eating disorder or experienced disordered eating behaviors, or if you’re immunocompromised, pregnant, lactating, or on insulin, oral hypoglycemic, or food-metabolizing medications. No matter who you are: Always check with your doctor before starting any new diet plan — especially one that includes fasting!
While some research tells us that there may be potential benefits for certain dieters, if severe food restrictions provoke any anxiety, then just don’t do it. There’s no clear-cut reason to opt out of meals, so stick with consistent eating strategies that work best for you — without any shame or guilt that extreme behaviors can stir up in so many of us.
Is intermittent fasting good for you?
Intermittent fasting could help you cut back on late-night snacking and get off to bed sooner, both major upsides when it comes to weight loss. Aleksandra BaranovaGetty Images
What I like about intermittent fasting is that there may be benefits for some people to prolong (realistically) the time they go without food as it relates to sleep and caloric intake.
More purposeful eating: The biggest advantage of intermittent fasting stems from the fact many of us eat based on the scenario, not hunger levels. (Raise your hand if you’ve ever gone to the movies after dinner and suddenly wanted popcorn.) Through IF, you’re limiting when you’re allowed to eat, meaning you cut back on habit-driven snacking you may not have been aware of. Say you’re a person who loves to graze during The Bachelor; if you’re “fasting” post 8 p.m., you’ve automatically cut out munching opportunities — and subsequently, calories.
Better sleep habits: If your fasts are time-restricted, the lack of late-night snacking alone could help you go to bed earlier — a crucial component to any weight-loss plan. Getting seven hours of sleep per night has been linked to weight management, reduced risk of chronic disease, and improved metabolism. Plus, a July 2019 study published in the International Journal of Obesity found that overweight individuals who were actively dieting and getting at least seven hours of sleep were able to lose more weight compared to those who were not.
Smarter food choices: Frequently choosing what and when to eat during a given day can leave us susceptible to making snap decisions that ultimately leave us dissatisfied — either immediately or when done consistently over time. But if you know you’ve only got a certain amount of time to eat, you may make smarter choices when you do. Simplifying and structuring the whole “what should I have for a snack?” scenario is a benefit many fasters appreciate.
How do you start intermittent fasting?
If you’re considering IF, I’d encourage you to start small and simple: Experiment with an “early bird special” for dinner. Close your kitchen once you’re finished, aim to get more sleep overnight, and eat a full breakfast at your usual time tomorrow. Making this one change is an aspect of intermittent fasting we can all get behind.
Jaclyn London, MS, RD, CDN, Good Housekeeping Institute Director, Nutrition Lab A registered dietitian with a Bachelor of Arts degree from Northwestern University and a Master of Science degree in Clinical Nutrition from New York University, Jaclyn “Jackie” London handles all of Good Housekeeping’s nutrition-related content, testing, and evaluation.
Unless you live under a rock, I’ll bet you have at least one friend who swears by intermittent fasting (IF). Or if you’re the kind of person who is a devoted celeb follower on IG, then you’ve definitely seen folks there talk about how much they love the buzzy eating plan, from Kourtney Kardashian to keto devotee Jenna Jameson.
Basically, intermittent fasting calls for restricting eating to certain time periods within a given day or week. Some plans call for certain fasting windows (time periods where a person can and cannot eat), while others have people eating every day but some days have a lower caloric intake than others.
The concept of skipping meals or limiting how much you eat at given times sounds…well, dicey. But proponents of the eating plan posit that by putting the body into a fasting state for short periods of time, people can potentially boost their metabolism, kickstart healthy weight loss, and see other intermittent fasting benefits like enhanced cognition and improved energy and mood.
However, exactly how the diet works is a hot debate among researchers, says James Mitchell, Ph.D., associate professor at Harvard T.H. Chan School of Public Health, whose research focuses on dietary restriction. Many people believe that both the potential metabolic benefits and weight loss are just a result of calorie restriction (eating less overall), while again, others believe that going set periods of time without eating plays a role. And while people who practice IF swear by its benefits, what they don’t talk about is how that anecdotal evidence isn’t totally backed up by research…yet.
So yeah, there’s a lot to unpack with the buzzy eating plan. Here’s what you should know about intermittent fasting before considering it for yourself:
The three most popular types of intermittent fasting are 16:8, 5:2, and alternate-day fasting.
In 16:8 fasting (also known as Leangains), you restrict eating to a specific eight-hour window every day, so that you’re essentially fasting for 16 hours every day. You choose what your hours are—if you like to eat dinner late, for example, you could choose to have your first meal of the day at 1 p.m., and not eat any more food for the day after 9 p.m. No foods are off-limits, but the idea is that you shouldn’t eat bigger meals than you normally would during the eight hours.
“I think this time-restricted feeding paradigm is the one with highest compliance,” says Dr. Mitchell. “It’s compatible with a busy lifestyle—you get up, skip breakfast, have a late lunch, and eat dinner with everybody. That’s doable most days.”
On the 5:2 diet, you eat normally five days per week, and reduce calorie intake to 500-600 calories for two non-consecutive days per week of your choosing. The diet authors emphasize that during the five “normal” eating days you should eat as you would if you weren’t fasting part of the time, and there are no rules on what you can and can’t eat. The diet can be tough to stick to—500 calories doesn’t go far in a day, especially if you’re active or busy.
Strictest of all is alternate-day fasting, or ADF. It’s just as it sounds: You fast every other day, continuously. Some people do full-on water fasts, while others choose to eat around 500 calories on fasting days. Because this version of IF is so restrictive, it’s not recommended for most people unless they’re under the advisement of a doctor and a dietitian. Plus, studies have shown that in alternate-day fasting, people don’t typically adapt to be less hungry during the fasting periods—making it very difficult to stick with.
Watch the video below to see a registered dietitian weigh in on intermittent fasting:
Intermittent fasting may help with weight management, but isn’t a guarantee.
Intermittent fasting will likely lead to some weight loss in the short-term because people generally eat fewer calories on this plan, whether or not they are following a form of IF that specifically calls for limited-calorie days. “With time-restricted feeding, the thinking is that you can eat as much of whatever you want, as long as it’s during a narrower window,” Dr. Mitchell says. “Of course, what happens in reality is that people generally don’t eat as much—it feels good to think that you can, but you really can’t, consistently, if you’re eating during a shorter window.”
However, current research doesn’t support any long-term weight management potential with intermittent fasting. Although a 2017 review found that a majority of studies reviewed (11 out of 17) showed statistically significant weight loss, none were long-term or large-scale, meaning their results aren’t entirely conclusive. (The longest of these 11 lasted 20 weeks and included just 54 subjects; the shortest lasted one day (one day!) and included 30 people, which, kay). The longest and largest study examined in the review lasted for six months and included 107 young, overweight females…but no significant weight-loss results were reported.
So in short: “IF may help reduce weight, but it works because in the end, it’s a low-calorie diet,” says Abby Langer, R.D.
Intermittent fasting benefits for hormones and metabolism are promising, but inconclusive.
Although anecdotal evidence—what you’ve heard from friends and wellness influencers—make IF seem like a magic bullet for improved health, the actual research is still in early stages. Since there isn’t just one definition for IF (see above with the different types of plans), it’s up to individual research teams to define its parameters for different studies. “Researchers really haven’t compared the different types of intermittent fasting,” says Dr. Mitchell. It’s difficult to find funding for such granular, descriptive studies, he says.
One agreed-upon benefit, says Dr. Mitchell, is that occasional fasting can improve insulin sensitivity—which is key to metabolic health, diabetes prevention, and weight management.
Many other studies looking at IF’s impact on hormones have been done on animals, or on very small (generally less than ten) groups of healthy people—making the results not super conclusive. Likewise, a 2015 review of the literature found that, while IF definitely has potential and warrants further study, there’s little published data that effectively links this eating style to better health outcomes in terms of diabetes, heart health, cancer, or other chronic diseases. But there is promise: A 2017 study of 100 people found that those who did a fasting-style diet for five days in a row per month lost weight, lowered their blood pressure, and saw other improvement in markers for age-related diseases.
As for the purported brain-boosting benefits of intermittent fasting? Take those with a grain of salt; published studies have been only done on animals. But there is some evidence that switching back and forth from a fasted state could boost brain function and help it fight off disease.
Although IF might be OK for some people, it’s definitely not for everybody.
For anyone who has a history of eating disorders or disordered eating: “Stay far away ,” says Langer. The National Eating Disorder Association (NEDA) lists both history of dieting and a negative energy balance (burning more calories than you’re taking in) as biological risk factors for an eating disorder. “Many people report that their disorder began with deliberate efforts to diet or restrict the amount and/or type of food they were eating in the form of dieting,” the group says. Although IF doesn’t restrict types of food, it’s definitely a form of food restriction.
As with any diet, timing matters—if someone is sick or recovering from an injury, IF should be put to the side. “If you’re trying to heal a wound, it might work against you,” Dr. Mitchell says. Adequate nutrition, especially protein, is important for healing, so whether you’re healing from surgery or just a scrape, the best thing to do is eat without restriction until you’re back to normal. Same goes for those who have a preexisting health condition like a thyroid disorder—going without nutrients for longer periods of time might be riskier for them.
Also keep in mind that social isolation might be an issue. “Some days you’ll finish eating before typical dinner reservations! The timing can get tricky,” says Langer.
Bottom line: While we’ve still got plenty to learn about IF, the potential weight management and health benefits might be worth it for some people. But given its restrictive nature, it’s definitely not an eating plan for everyone.
Another popular eating plan this time of year: Whole30. Check out the video below to see what a registered dietitian thinks of it:
Originally published March 24, 2019. Updated January 2, 2020.
If you’re curious about other trendy eating plans, you should read up on the ketogenic diet and the Paleo diet.
Fasting: Health benefits and risks
Fasting is commonly associated with the month of Ramadan. As you read this, billions of Muslims around the world are engaging in this declaration of faith that involves abstaining from food and drink from dawn until dusk. While fasting for Ramadan is down to spiritual beliefs, many of us choose to fast with the belief that it benefits our health. But does it?
Share on PinterestA number of studies have suggested intermittent fasting has numerous health benefits, including weight loss, lower blood pressure and reduced cholesterol.
In recent years, numerous studies have suggested that intermittent fasting – abstaining or reducing food and drink intake periodically – can be good for us, making it one of the most popular diet trends worldwide.
One of the most well-known intermittent fasting diets is the 5:2 Fast Diet – a plan that involves eating the recommended calorie intake for 5 days a week but reducing calorie intake to 25% for the remaining 2 days – to 500 calories a day for women and 600 a day for men.
According to Dr. Michael Mosley – author of The Fast Diet books – this eating plan can not only help people lose weight, but it offers an array of other health benefits.
“Studies of intermittent fasting show that not only do people see improvements in blood pressure and their cholesterol levels, but also in their insulin sensitivity,” he adds.
In June 2014, for example, Medical News Today reported on a study suggesting periodic fasting – defined in the study as 1 day of water-only fasting a week – may reduce the risk of diabetes among people at high risk for the condition.
Another study, conducted by Dr. Valter Longo and colleagues from the University of Southern California (USC) in Los Angeles, found longer periods of fasting – 2-4 days – may even “reboot” the immune system, clearing out old immune cells and regenerating new ones – a process they say could protect against cell damage caused by factors such as aging and chemotherapy.
But what are the mechanisms underlying the suggested health benefits of fasting?
The potential benefits of intermittent fasting
Since the body is unable to get its energy from food during fasting, it dips into glucose that is stored in the liver and muscles. This begins around 8 hours after the last meal is consumed.
When the stored glucose has been used up, the body then begins to burn fat as a source of energy, which can result in weight loss.
As well as aiding weight loss, Dr. Razeen Mahroof, of the University of Oxford in the UK, explains that the use of fat for energy can help preserve muscle and reduce cholesterol levels.
Share on PinterestWhen the body has used up glucose stores during fasting, it burns fat for energy, resulting in weight loss.
“A detoxification process also occurs, because any toxins stored in the body’s fat are dissolved and removed from the body,” he adds, noting that after a few days of fasting, higher levels of endorphins – “feel-good” hormones – are produced in the blood, which can have a positive impact on mental well-being.
As mentioned previously, the study by Dr. Longo and colleagues suggests prolonged fasting may also be effective for regenerating immune cells.
“When you starve, the system tries to save energy, and one of the things it can do to save energy is to recycle a lot of the immune cells that are not needed, especially those that may be damaged,” Dr. Longo explains.
In their study, published in the journal Cell Stem Cell, the team found that repeated cycles of 2-4 days without food over a 6-month period destroyed the old and damaged immune cells in mice and generated new ones.
What is more, the team found that cancer patients who fasted for 3 days prior to chemotherapy were protected against immune system damage that can be caused by the treatment, which they attribute to immune cell regeneration.
“The good news is that the body got rid of the parts of the system that might be damaged or old, the inefficient parts, during the fasting,” says Dr. Longo. “Now, if you start with a system heavily damaged by chemotherapy or aging, fasting cycles can generate, literally, a new immune system.”
With the potential health benefits of fasting widely hailed by nutritionists worldwide, it is no wonder many of us are putting our love of food to one side in order to give it a try.
But intermittent fasting isn’t all bells and whistles, according to some researchers and health care professionals, and there are some people who should avoid the diet altogether.
The health risks of fasting
According to the UK’s National Health Service (NHS), there are numerous health risks associated with intermittent fasting.
People who fast commonly experience dehydration, largely because their body is not getting any fluid from food. As such, it is recommended that during Ramadan, Muslims consume plenty of water prior to fasting periods. Other individuals following fasting diets should ensure they are properly hydrated during fasting periods.
If you are used to having breakfast, lunch, dinner and snacks in between, fasting periods can be a major challenge. As such, fasting can increase stress levels and disrupt sleep. Dehydration, hunger or lack of sleep during a fasting period can also lead to headaches.
Fasting can also cause heartburn; lack of food leads to a reduction in stomach acid, which digests food and destroys bacteria. But smelling food or even thinking about it during fasting periods can trigger the brain into telling the stomach to produce more acid, leading to heartburn.
While many nutritionists claim intermittent fasting is a good way to lose weight, some health professionals believe such a diet is ineffective for long-term weight loss.
“The appeal is that is quick, but it is quick fluid loss, not substantial weight loss,” says Madelyn Fernstrom, PhD, of the University of Pittsburgh Medical Center’s Weight Loss Management Center. “If it’s easy off, it will come back quickly – as soon as you start eating normally again.”
“My experience has been that way of eating does not produce weight loss even in the short term,” dietitian and author of Diet Simple Katherine Tallmadge told ABC News in 2013.
Some health professionals believe intermittent fasting may steer people away from healthy eating recommendations, such as eating five portions of fruits and vegetables a day. Many fear fasting may also trigger eating disorders or binge eating.
In a blog for The Huffington Post last year, fitness and nutrition expert JJ Virgin wrote:
“The ‘anything goes’ mentality some experts permit during the feeding state could lead someone to overeat, creating guilt, shame, and other problems that only become worse over time. For someone with emotional or psychological eating disorders, intermittent fasting could become a convenient crutch to amplify these issues.”
While Dr. Mosely says there is no evidence to suggest the 5:2 Fast Diet is associated with eating disorders, he stresses people who have eating disorders should not engage in intermittent fasting.
Other people who should not follow this diet include people who are underweight, individuals under the age of 18, pregnant women, people with type 1 diabetes and individuals recovering from surgery.
Could we reap the benefits of fasting without fasting?
While intermittent fasting may have health risks, nutritionists claim it can be good for us if individuals consult with their doctors before adopting such a diet and adhere to it correctly.
But could there be a way to reap the potential health benefits of fasting without actually having to fast? Dr. Longo believes so.
Share on PinterestResearchers say a fasting-mimicking diet could simulate the effect of fasting without the food deprivation and side effects.
Earlier this week, Dr. Longo and colleagues from USC published a study in the journal Cell Metabolism revealing how a fasting-mimicking diet (FMD) triggered immune cell regeneration and extended the lifespan of mice.
What is more, on testing the diet in humans – who adhered to it for only 5 days a month for 3 months – they found it reduced a number of risk factors associated with aging, cardiovascular disease (CVD), diabetes and cancer.
The FMD is low in protein, low in unhealthy fats and high in healthy fats, according to the researchers. It stimulates markers linked to fasting, such as low glucose levels and high levels of ketone bodies, in order to mimic the effects of prolonged fasting.
Dr. Longo and colleagues say their diet could promote immune cell regeneration and longevity associated with fasting without the need for food restriction and the potential adverse effects that come with it.
“Although the clinical results will require confirmation by a larger randomized trial,” they add, “the effects of FMD cycles on biomarkers/risk factors for aging, cancer, diabetes, and CVD, coupled with the very high compliance to the diet and its safety, indicate that this periodic dietary strategy has high potential to be effective in promoting human healthspan.”
The team hopes that clinicians will one day have the ability to prescribe this diet to patients. “This is arguably the first non-chronic preclinically and clinically tested anti-aging and healthspan-promoting intervention shown to work and to be very feasible as a doctor or dietitian-supervised intervention,” says Dr. Longo.
It may be a while before the FMD receives approval from the US Food and Drug Administration (FDA) for clinical use. First, the team needs to put the diet through a rigorous testing process.
Further research is required to gain a better understanding of the exact benefits and risks the FMD poses, and this appears to be the case with existing fasting diets. One thing is clear, however; talk to your doctor before engaging in any form of fasting.
The evidence just keeps growing in favor of intermittent fasting — and not just for weight loss.
Studies and clinical trials have shown the eating regimen has “broad-spectrum benefits” for health problems including obesity, diabetes, heart disease, cancer and neurologic disorders, researchers wrote in a new review of research in humans and animals.
The paper was published Wednesday in the New England Journal of Medicine.
The powerful health effects appear to come from the body flipping a “metabolic switch” during fasting — or shifting away from using sugar as its main source of energy and instead converting fat for fuel when a person’s stomach is empty.
But most people still eat all throughout the day and miss out on the health benefits, said lead author Mark Mattson, adjunct professor of neuroscience at the Johns Hopkins University School of Medicine.
Is intermittent fasting for you? Dr. Oz explains the pros and cons
Nov. 14, 201904:20
“The evidence is accumulating that this metabolic switch triggers a lot of signaling pathways in cells and various organs that improve their stress resistance and resilience,” Mattson, who has been practicing intermittent fasting for 30 years, told TODAY.
“If you eat three meals a day plus snacks spaced out… you may never have that metabolic switch occurring.”
Many patients ask their doctors about intermittent fasting, but the physicians themselves are often not up on the science, which has rapidly progressed, he added. Medical schools still aren’t teaching future doctors about the benefits, but Mattson is hopeful that will change with time.
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What the science shows:
When a person depletes his or her sugar energy stores during fasting, fats are released from fat cells and converted to ketone bodies by the liver.
Ketone bodies aren’t just an energy source, but also have a “potent signaling” function. The body responds by activating certain pathways that boost beneficial processes like autophagy, a mechanism that helps to regenerate cells. These pathways are untapped or suppressed in people who overeat and are sedentary, the review noted.
When a person switches between a fed and fasted state, it stimulates responses that boost mental and physical performance, plus disease resistance, the authors wrote.
“We’re adapted through millions of years of evolution to respond to reduced food availability in ways that one, enable us to get food, but two, increase our ability to resist various types of environmental stress,” Mattson said.
Benefits of intermittent fasting revealed in new study
Aug. 28, 201903:48
Studies in humans show intermittent-fasting helps reduce obesity, insulin resistance, high cholesterol, high blood pressure and inflammation. It can improve verbal memory, executive function and global cognition in adults with mild cognitive impairment.
No studies have yet determined whether intermittent fasting affects cancer recurrence in humans, but research in animals has shown it reduces the number of spontaneous tumors during aging.
The weight-loss factor is also a major draw: Intermittent fasting can help people slim down without having to count calories, “so psychologically it seems a little easier,” Mattson said.
How to adopt intermittent fasting in your life:
There are three most-widely studied types of intermittent fasting:
- daily time-restricted feeding, where you fast for a certain amount of hours a day, often 16, but are free to eat whatever you want the rest of the time. This is the easiest for most people to adopt, Mattson said. It’s the regimen he follows: He skips breakfast, exercises mid-day, then eats all his food between 1 p.m. and 7 p.m.
- the 5:2 plan, which means incorporating two non-consecutive fast days into your week, then eating normally during the other days.
- alternate day fasting, which means eating nothing or very little one day, then eating whatever you want the next, and then repeating that process.
“A lot of people who try to switch to intermittent fasting don’t realize it takes a while to adapt,” Mattson noted. They may experience hunger and irritability at first, but those side effects usually disappear within a month.
Ease into it, the review advised. For daily time-restricted feeding, start with an eating window of 12 hours, then gradually reduce it to ten, eight or even six hours over several months.
For the 5:2 plan, start by eating about 1,000 calories one day a week for the first month, then try it for two days a week for the second month. Limit those two fasting days to 750 calories each for the third month and, ultimately, 500 calories for the fourth month.
Always check with your doctor and a nutritionist before starting an intermittent fasting regimen.
Companies are now working on a wrist device that would let people monitor their ketones and know in real time whether the metabolic switch has occurred, Mattson said. Once people try intermittent fasting, many see a host of benefits and never go back to three meals a day — just like him.
“A lot of people I know have tried it and like it and have stuck with it,” he noted.
You know the drug in the movie Limitless? Fasting is the natural, healthy, and sustainable version of that.
1. Superhuman Willpower
Fasting, by its very nature, is the putting-off of the physical in order to tap into higher realms of meaning.
Destructive addictions and other sabotaging behaviors are the opposite of willpower. And they slowly but surely ruin your life.
Every decision you make is important. If you justify poor decisions from time-to-time, you’re stunting the development of quality habits. More accurately, consistent poor behavior is in actuality the reflection of bad habits.
And bad habits are a fast-track to a crappy life — the root of which is a lack of self-control.
If you can’t control even yourself, what can you control?
But while you’re fasting, you are consciously choosing not to eat — even if you feel hungry — for something else. And there’s nothing more fundamental to survival than food. Consequently, when you learn to control your own eating, you develop the ability to control less fundamental and often destructive addictions.
Fasting is by far the most sophisticated willpower workout available. If you get good at fasting, you can learn to control every other aspect of your life. If you get good at fasting, you can overcome any addiction, not matter how deeply imbedded. Medically, fasting has been found to rapidly dissipate the craving for nicotine, alcohol, caffeine and other drugs.
2. Superhuman Confidence
Neuro-chemically, fasting increases levels of catecholamines — such as dopamine — which elevates your happiness and confidence while reducing your anxiety.
But it’s simpler than that.
Without self-control, you can’t have confidence. Indeed, confidence reflects your view of your own capability. And if you constantly self-sabotage, rather than confidence you’ll experience internal-conflict.
Internal-conflict corrodes your willpower. It’s exhausting and leaves you constantly on the defensive — both to other people and yourself.
But when you see yourself act in ways you intended on acted, your confidence in yourself increases. You develop greater trust in your own capabilities, and this prompts you to take on bigger goals, risks, and challenges in the future. Eventually, you develop the self-efficacy that allows you to control your destiny and future. Complete power and confidence.
3. Superhuman Brain Functioning
Fasting actually increases your number of brain cells. Here is a short list of some of the scientifically backed cognitive benefits of fasting:
· Short-term fasting induces profound neuronal autophagy (e.g., “self-eating,”), which is how cells recycle waste material, downregulate wasteful processes, and repair themselves. Brain health is dependent on neuronal autophagy. Another study shows that interference of neuronal autophagy prompts neuro-degeneration. Simply put, without the process of autophagy, brains neither develop properly nor function optimally.
· Fasting increases levels of brain-derived neurotrophic factor (BDNF), a protein that interacts with neurons in the hippocampus, cortex, and basal forebrain (the parts of the brain that regulate memory, learning, and higher cognitive function — uniquely human stuff). BDNF helps existing neurons survive while stimulating the growth of new neurons and the development of neuro-synaptic connectivity. Low levels of BDNF are linked to Alzheimer’s, memory loss, and cognitive impairment.
· Evidence suggests that low BDNF is related to depression. Indeed, antidepressants increase BDNF levels. Thus, many doctors believe fasting can reduce depression.
· Fasting reduces the likelihood of having a stroke.
· Fasting reduces the oxidative stress, mitochondrial dysfunction, and cognitive decline that normally results from brain trauma. Research has found that a 24 hour (but not a 48 hour) fast was neuro-protective against trauma to the brain like a concussion.
· Fasting reduces cognitive stressors that bring about aging, cognitive decline, and chronic diseases.
· Fasting reduces your risk of cancer.
· Fasting increases your longevity and lifespan.
· Fasting enhances learning and memory.
· Fasting elevates your ability to focus and concentrate.
If you’ve fasted before, you can attest to the radical mental benefits of fasting. If you haven’t, please start a regular practice of fasting. Over a period of time, you’ll be startled by the cognitive results.
4. Superhuman Clarity & Direction
With the increased clarity and cognitive functioning brought on by fasting, it is easier to analyze your poor habits and make critical decisions about the direction of your life.
When you remove yourself from the noise of addiction — even food addiction temporarily — you clear space for the subtle signal of your guiding truth.
While fasting, you will quickly become aware of the incongruencies in your life. Your poor habits, lack of organization and intention, and misdirected path get put under a cognitive and spiritual microscope.
With increased perspective and willpower, you can use fasting as a vehicle to “let go” of addictions, behaviors, relationships, the past — whatever you want — restart, and move forward. Physically, cognitively, emotionally, and spiritually, fasting is quite literally a reset. It allows your body to catch up on needed digestive functions it generally delays due to our constant eating. But it also helps you reset in other ways.
Fasting can become your trigger to keeping proper perspective on what matters most in your life, and it helps ensure you remain on the path you desire to be on.
5. Superhuman Health
As a society, our brains have been miss-trained about the true nature of hunger, chemically tricking us into feeling hungry every 2–4 hours. But this is actually ludicrous. Naturally, our bodies shouldn’t experience hunger for 12–24 hours after eating.
Research has shown that obese individuals do not receive correct signals letting them know they are full due to excessive eating patterns. Their neuro-chemicals and hormones are all out of whack due to improper eating.
As you fast, your body regulates the release the correct hormones, so that you can experience what real hunger is. Further, with the proper flow of hormones, you get full quicker.
Other scientifically backed health benefits of fasting including:
· Fasting can reverse binge eating disorders, and help those who find it difficult to establish a correct eating pattern due to work and other priorities.
· Fasting can clear your skin from acne, allowing you to have a healthy vibrant glow.
· Fasting “reboots” your immune system from free radical damage, regulating inflammatory conditions in the body and killing-off cancer cell formation.
· Fasting improves blood pressure levels.
· Fasting improves cholesterol levels.
· Type 2 diabetes has become commonplace in our unhealthy culture. Fasting has been shown to strongly support insulin resistance and lead to an impressive reduction in blood sugar levels.
· Similarly, blood levels of insulin drop significantly, which facilitates fat burning.
· The blood levels of growth hormone may increase as much as 5X. Higher levels of growth hormone assist fat burning and muscle gain, and have numerous other benefits.
Not only will your body functioning improve as you fast, but your decision-making regarding your health and fitness will improve.
6. Superhuman Motor Skills & Precision
Research has found that age-related declines in cognitive and motor abilities (such as physical balance) can be reduced by fasting.
My 93 year old grandfather, Rex, is an incredible example of this. As a Mormon, he has had the regular practice of doing a 24 hour fast, monthly, his entire life. He attributes his longevity and healthy brain and motor functioning in large part to his regular practice of fasting.
It’s fun to watch him. In the past five years, he’s written three books. He lives with his son (my father) and takes responsibility over mowing the lawn weekly and making sure the yard work is done. He has an amazing daily routine of going to bed at 8 P.M. and waking up at 4:30 A.M. every day. He spends the first 2.5 hours of his day reading or listening to instructional/inspiring content. He eats a bowl of oatmeal at 7 o’clock sharp, then he works until about 2 P.M. every day. He even sets timers every hour to allow him a 10 minute Solitaire break (which is also timed). The second the timer goes off, he gets back to work.
All those incredible habits and he attributes fasting to be a crucial needle, threading them all together and making them all possible.
7. Superhuman Sleep
If you travel a lot or have a lackluster sleeping cycle, research has found that a 16-hour fast can reset your sleep cycle. Other research has found that fasting can improve the overall quality of your sleep.
8. Superhuman Productivity
“If you want to get more done in life, eat less food.” — Robin Sharma, best-selling author
Human beings are holistic. When your body is over-full, particularly on processed foods, your energy levels are low and your mind becomes dull. Conversely, research at Yale has found that being on an empty stomach helps you think and focus better.
While you’re fasting, if you want to take it to a higher level, chew gum. Research has found that chewing gum can increase your concentration and mental accuracy. It also stops you from eating out of boredom — which is the primary reason for most eating.
In a fasted state, your mind can narrow in on your work. I believe this is because the cognitive and sensual amplification of fasting forces you into the moment. In other words, fasting helps you live in the present. It’s powerful and beautiful. High focus and psychological flow are commonplace for me while I fast.
9. Superhuman Emotions
Fasting stabilizes your emotions. This happens by detaching from the emotional dependence on food, in addition to removing over-stimulating foods like caffeine, processed sugars, recreational drugs, tobacco and trans-fatty acids — all of which negatively effect our emotions.
Fasting can also reset your negative emotional patterns. We all get locked-up in weird emotional cycles, and fasting can break us free of them — allowing us to experience the world in a healthier way. It’s also important to note that our emotions are heavily influenced by our environments — and fasting allows us to perceive the incongruencies of our life more clearly — thus challenging us to reshape our environments.
10. Superhuman Energy
Fasting gives you a feeling a physical “lightness,” which provides a boost of energy. Another reason for this energy-surge is because, in a normal diet, our body generally converts foods through carbs and sugars. But fasting retrains our body to convert energy from fats, thus boosting our natural energy levels.
11. Superhuman Weight Loss
Fasting has facilitate weight-loss of 3–8 percent of total body mass in just 3–24 weeks! During that same time-frame, you could lose 4–7 percent of your waist circumference (e.g., harmful belly fat that causes disease).
Fasting decreases insulin levels, while boosting growth hormone levels and increased quantities of norepinephrine (noradrenaline) — a hormonal coctail that breaks down body fat and enables its use for energy.
Consequently, fasting actually increases your metabolic rate by 4–14 percent, helping you burn more calories.
12. Superhuman Inspiration
Fasting taps into higher realms than merely increased consciousness. My experience with fasting is physical, emotional, cognitive, and spiritual. And I leverage fasting for all it’s worth. I openly pray while fasting for miracles and blessings to come into my life and the into the lives of people I care for.
And I genuinely believe it works.
Regardless of the source of my inspiration, I keep my journal and pen constantly at my side while I’m fasting. The majority of my ideas for writing come while I’m fasting. It’s like drinking from a firehose. “My cup runneth over.”
If you’re looking for mental and spiritual breakthroughs — or simply an increased free-flow of intelligence — regular fasting will aid you in this.
13. Superhuman Appearance
Fasting clears the skin and whitens the eyes. It is common to see acne clear while fasting; and the whites of the eyes never look so piercingly clear and bright as they do after fasting.
The reason for this is the release of human growth hormone, which has been found to make your skin look younger and more vibrant.
But it’s even simpler than that. When you’re living a life of self-control, your health and confidence shine through. You smile more, laugh more, and are more perceptive and discerning of others. Human beings are holistic. When we’re out of alignment, it’s actually quite apparent to others. When we are in alignment, it couldn’t be more obvious. You will simply look more attractive by resonating on a higher physical, cognitive, emotional, and spiritual plane.
14. Superhuman Learning
Research confirms that being in a fasted state improves focus, memory, and ability to comprehend information.Put most simply, fasting improves brain efficiency and effectiveness.
15. Superhuman Senses
It’s easy to get addicted to sugary foods. When we do, we stop craving healthy, earthy, and wholesome foods. But fasting restores our appreciation for these delicious flavors. Your taste-buds become electric after fasting, and eating healthy foods never tasted so good.
Beyond taste, fasting increases the acuity of all your other senses as well, including hearing and smell, and sometimes even vision.
Actually, it can be a startling experience when your brain functioning radically elevates during a fast. Your listening skills sharpen, and you focus in on every word the other person is saying. Your thinking is honed and your ability to quickly and accurately respond is dynamite.
You can hear the slightest sounds in your natural environment which you are usually unaware of.
Time slows down.
Everything is heightened. The colors you see, the sounds you hear, the thoughts bouncing around in your head, your connection to your physical body and external environment.
If you resonated with these ideas, please subscribe to my person blog. You will get a free copy of my eBook Slipstream Time Hacking, which blends ideas from astrophysics, psychology, and entrepreneurship.
Is fasting an effective weight-loss method?
If you are obese or overweight, fasting is an effective weight-loss method, if you stick to it. But it is no more effective than a diet that restricts your daily calories. We know this because there were no additional weight-loss or cardiovascular benefits of fasting two days per week, over an ordinary calorie-restriction diet, in a study of 150 obese adults over the course of 50 weeks.
But you should also consider how difficult the diet will be to stick to. In a study of 100 randomized obese and overweight adults published in 2017, the dropout rate was higher with those who were fasting, 38 percent, compared with 29 percent for calorie restrictors and 26 percent for those who kept eating as they normally did.
“Some people really struggle with having to monitor their intake and constantly record food in an app every day. So the takeaway of the study was if daily calorie restriction doesn’t work for you, maybe alternate-day fasting would be a little easier,” said Krista Varady, Ph.D., professor of nutrition at the University of Illinois at Chicago and the senior author of the study. “There’s nothing magical here. We’re tricking people into eating less food, in different ways,” she said in 2017.
There is some new evidence that shows different forms of fasting are not equal — in part because some are easier than others, but also because some forms of fasting better match our body’s natural circadian rhythm, thus lowering insulin levels, increasing fat-burning hormones and decreasing appetite.
Basically, because our metabolism has evolved to digest food during the day and rest at night, changing the timing of meals to earlier in the day may be beneficial.
In a study done in Dr. Peterson’s lab, 11 adults did time-restricted feeding (eating from 8 a.m. to 2 p.m.) and a control 12-hour eating period, for four days each. On the last day of each session, researchers measured energy expenditure and hunger hormones and found that time-restricted feeding improves the appetite hormone ghrelin and increases fat burning. “It’s shown to reduce the amount of fat in the liver, which is a risk factor for diabetes and cardiovascular disease,” said Dr. Peterson.
I have been intermittent fasting for over one year.
I skip breakfast each day and eat two meals, the first around 1pm and the second around 8pm. Then, I fast for 16 hours until I start eating again the next day at 1pm.
Surprisingly, since I’ve started intermittent fasting I’ve increased muscle mass (up 10 pounds from 205 to 215), decreased body fat (down 3% from 14% to 11%), increased explosiveness (set a personal best with a clean and jerk of 253 pounds a few months back), and decreased the amount of time I’ve spent training (down from 7.5 hours per week to 2.5 hours per week).
In other words, I’m stronger, leaner, and more explosive even though I go to the gym less and eat less.
You may be wondering…
How is this possible? Isn’t skipping breakfast bad for you? Why would anyone fast for 16 hours every day? What are the benefits? Is there any science behind this or are you just crazy? Is it dangerous?
Slow down, friend. I’ve been known to do some crazy things, but this is totally legit. It’s easy to implement into your lifestyle and there are tons of health benefits. In this post, I’m going to break down intermittent fasting and everything that goes with it.
Free Bonus: I created an Intermittent Fasting Quick Start Guide with a summary of the benefits of intermittent fasting and 3 fasting schedules you can use depending on your goals. It’s a quick 5 page PDF you can save and reference later as you try this yourself. .
What is Intermittent Fasting and Why Would You Do It?
Intermittent fasting is not a diet, it’s a pattern of eating. It’s a way of scheduling your meals so that you get the most out of them. Intermittent fasting doesn’t change what you eat, it changes when you eat.
Why is it worthwhile to change when you’re eating?
Well, most notably, it’s a great way to get lean without going on a crazy diet or cutting your calories down to nothing. In fact, most of the time you’ll try to keep your calories the same when you start intermittent fasting. (Most people eat bigger meals during a shorter time frame.) Additionally, intermittent fasting is a good way to keep muscle mass on while getting lean.
With all that said, the main reason people try intermittent fasting is to lose fat. We’ll talk about how intermittent fasting leads to fat loss in a moment.
Perhaps most importantly, intermittent fasting is one of the simplest strategies we have for taking bad weight off while keeping good weight on because it requires very little behavior change. This is a very good thing because it means intermittent fasting falls into the category of “simple enough that you’ll actually do it, but meaningful enough that it will actually make a difference.”
How Does Intermittent Fasting Work?
To understand how intermittent fasting leads to fat loss we first need to understand the difference between the fed state and the fasted state.
Your body is in the fed state when it is digesting and absorbing food. Typically, the fed state starts when you begin eating and lasts for three to five hours as your body digests and absorbs the food you just ate. When you are in the fed state, it’s very hard for your body to burn fat because your insulin levels are high.
After that timespan, your body goes into what is known as the post–absorptive state, which is just a fancy way of saying that your body isn’t processing a meal. The post–absorptive state lasts until 8 to 12 hours after your last meal, which is when you enter the fasted state. It is much easier for you body to burn fat in the fasted state because your insulin levels are low.
When you’re in the fasted state your body can burn fat that has been inaccessible during the fed state.
Because we don’t enter the fasted state until 12 hours after our last meal, it’s rare that our bodies are in this fat burning state. This is one of the reasons why many people who start intermittent fasting will lose fat without changing what they eat, how much they eat, or how often they exercise. Fasting puts your body in a fat burning state that you rarely make it to during a normal eating schedule.
The Benefits of Intermittent Fasting
Fat loss is great, but it isn’t the only benefit of fasting.
1. Intermittent fasting makes your day simpler.
I’m big on behavior change, simplicity, and reducing stress. Intermittent fasting provides additional simplicity to my life that I really enjoy. When I wake up, I don’t worry about breakfast. I just grab a glass of water and start my day.
I enjoy eating and I don’t mind cooking, so eating three meals a day was never a hassle for me. However, intermittent fasting allows me to eat one less meal, which also means planning one less meal, cooking one less meal, and stressing about one less meal. It makes life a bit simpler and I like that.
2. Intermittent fasting helps you live longer.
Scientists have long known that restricting calories is a way of lengthening life. From a logical standpoint, this makes sense. When you’re starving, your body finds ways to extend your life.
There’s just one problem: who wants to starve themselves in the name of living longer?
I don’t know about you, but I’m interested in enjoying a long life. Starving myself doesn’t sound that appetizing.
The good news is that intermittent fasting activates many of the same mechanisms for extending life as calorie restriction. In other words, you get the benefits of a longer life without the hassle of starving.
Way back in 1945 it was discovered that intermittent fasting extended life in mice. (Here’s the study.) More recently, this study found that alternate day intermittent fasting led to longer lifespans.
3. Intermittent fasting may reduce the risk of cancer.
This one is up for debate because there hasn’t been a lot of research and experimentation done on the relationship between cancer and fasting. Early reports, however, look positive.
This study of 10 cancer patients suggests that the side effects of chemotherapy may be diminished by fasting before treatment. This finding is also supported by another study which used alternate day fasting with cancer patients and concluded that fasting before chemotherapy would result in better cure rates and fewer deaths.
Finally, this comprehensive analysis of many studies on fasting and disease has concluded that fasting appears to not only reduce the risk of cancer, but also cardiovascular disease.
4. Intermittent fasting is much easier than dieting.
The reason most diets fail isn’t because we switch to the wrong foods, it’s because we don’t actually follow the diet over the long term. It’s not a nutrition problem, it’s a behavior change problem.
This is where intermittent fasting shines because it’s remarkably easy to implement once you get over the idea that you need to eat all the time. For example, this study found that intermittent fasting was an effective strategy for weight loss in obese adults and concluded that “subjects quickly adapt” to an intermittent fasting routine.
I like the quote below from Dr. Michael Eades, who has tried intermittent fasting himself, on the difference between trying a diet and trying intermittent fasting.
“Diets are easy in the contemplation, difficult in the execution. Intermittent fasting is just the opposite — it’s difficult in the contemplation but easy in the execution.
Most of us have contemplated going on a diet. When we find a diet that appeals to us, it seems as if it will be a breeze to do. But when we get into the nitty gritty of it, it becomes tough. For example, I stay on a low–carb diet almost all the time. But if I think about going on a low–fat diet, it looks easy. I think about bagels, whole wheat bread and jelly, mashed potatoes, corn, bananas by the dozen, etc. — all of which sound appealing. But were I to embark on such a low–fat diet I would soon tire of it and wish I could have meat and eggs. So a diet is easy in contemplation, but not so easy in the long–term execution.
Intermittent fasting is hard in the contemplation, of that there is no doubt. “You go without food for 24 hours?” people would ask, incredulously when we explained what we were doing. “I could never do that.” But once started, it’s a snap. No worries about what and where to eat for one or two out of the three meals per day. It’s a great liberation. Your food expenditures plummet. And you’re not particularly hungry. … Although it’s tough to overcome the idea of going without food, once you begin the regimen, nothing could be easier.”
— Dr. Michael Eades
In my opinion, the ease of intermittent fasting is best reason to give it a try. It provides a wide range of health benefits without requiring a massive lifestyle change.
Examples of Different Intermittent Fasting Schedules
If you’re considering giving fasting a shot, there are a few different options for working it into your lifestyle.
Daily Intermittent Fasting
Most of the time, I follow the Leangains model of intermittent fasting, which uses a 16–hour fast followed by an 8–hour eating period. This model of daily intermittent fasting was popularized by Martin Berkhan of Leangains.com, which is where the name originated.
It doesn’t matter when you start your 8–hour eating period. You can start at 8am and stop at 4pm. Or you start at 2pm and stop at 10pm. Do whatever works for you. I tend to find that eating around 1pm and 8pm works well because those times allow me to eat lunch and dinner with friends and family. Breakfast is typically a meal that I eat on my own, so skipping it isn’t a big deal.
Because daily intermittent fasting is done every day it becomes very easy to get into the habit of eating on this schedule. Right now, you’re probably eating around the same time every day without thinking about it. Well, with daily intermittent fasting it’s the same thing, you just learn to not eat at certain times, which is remarkably easy.
One potential disadvantage of this schedule is that because you typically cut out a meal or two out of your day, it becomes more difficult to get the same number of calories in during the week. Put simply, it’s tough to teach yourself to eat bigger meals on a consistent basis. The result is that many people who try this style of intermittent fasting end up losing weight. That can be a good thing or a bad thing, depending on your goals.
This is probably a good time to mention that while I have practiced intermittent fasting consistently for the last year, I’m not fanatical about my diet. I work on building healthy habits that guide my behavior 90% of the time, so that I can do whatever I feel like during the other 10%. If I come over to your house to watch the football game and we order pizza at 11pm, guess what? I don’t care that it’s outside my feeding period, I’m eating it.
Weekly Intermittent Fasting
One of the best ways to get started with intermittent fasting is to do it once per week or once per month. The occasional fast has been shown to lead to many of the benefits of fasting we’ve already talked about, so even if you don’t use it to cut down on calories consistently there are still many other health benefits of fasting.
The graphic below shows one example of how a weekly intermittent fast might play out.
In this example, lunch on Monday is your last meal of the day. You then fast until lunch on Tuesday. This schedule has the advantage of allowing you to eat everyday of the week while still reaping the benefits of fasting for 24 hours. It’s also less likely that you’ll lose weight because you are only cutting out two meals per week. So, if you’re looking to bulk up or keep weight on, then this is a great option.
I’ve done 24–hour fasts in the past (I just did one last month) and there are a wide range of variations and options for making it work into your schedule. For example, a long day of travel or the day after a big holiday feast are often great times to throw in a 24–hour fast.
Perhaps the biggest benefit of doing a 24–hour fast is getting over the mental barrier of fasting. If you’ve never fasted before, successfully completing your first one helps you realize that you won’t die if you don’t eat for a day.
Alternate Day Intermittent Fasting
Alternate day intermittent fasting incorporates longer fasting periods on alternating days throughout the week.
For example, in the graphic below you would eat dinner on Monday night and then not eat again until Tuesday evening. On Wednesday, however, you would eat all day and then start the 24–hour fasting cycle again after dinner on Wednesday evening. This allows you to get long fast periods on a consistent basis while also eating at least one meal every day of the week.
This style of intermittent fasting seems to be used often in research studies, but from what I have seen it isn’t very popular in the real world. I’ve never tried alternate day fasting myself and I don’t plan to do so.
The benefit of alternate day intermittent fasting is that it gives you longer time in the fasted state than the Leangains style of fasting. Hypothetically, this would increase the benefits of fasting.
In practice, however, I would be concerned with eating enough. Based on my experience, teaching yourself to consistently eat more is one of the harder parts of intermittent fasting. You might be able to feast for a meal, but learning to do so every day of the week takes a little bit of planning, a lot of cooking, and consistent eating. The end result is that most people who try intermittent fasting end up losing some weight because the size of their meals remains similar even though a few meals are being cut out each week.
If you’re looking to lose weight, this isn’t a problem. And even if you’re happy with your weight, this won’t prove to be too much of an issue if you follow the daily fasting or weekly fasting schedules. However, if you’re fasting for 24 hours per day on multiple days per week, then it’s going to be very difficult to eat enough of your feast days to make up for that.
As a result, I think it’s a better idea to try daily intermittent fasting or a single 24–hour fast once per week or once per month.
Frequently Asked Questions, Concerns, and Complaints
I’m a woman. Should I do anything differently?
I haven’t worked with women on implementing an intermittent fasting schedule, so I can’t speak from experience on this one.
That said, I have heard that women may find a wider window of eating to be more favorable when doing daily intermittent fasting. While men will typically fast for 16 hours and then eat for 8 hours, women may find better results by eating for 10 hours and fasting for 14 hours. The best advice I can give anyone, not just women, is to experiment and see what works best for you. Your body will give you signals. Follow what your body responds favorably to.
Also, if you’re a female, there is an all‐female page on Facebook that discusses intermittent fasting. I’m sure you could find a ton of great answers and support there.
I could never skip breakfast. How do you do it?
I don’t. Breakfast foods are my favorite, so I just eat them at 1pm each day.
Also, if you eat a big dinner the night before, I think you’ll be surprised by how much energy you have in the morning. Most of the worries or concerns that people have about intermittent fasting are due to the fact that they have had it pounded into them by companies that they need to eat breakfast or they need to eat every three hours and so on. The science doesn’t support it and neither do my personal experiences.
I thought you were supposed to eat every 3 hours?
You may have heard people say that you should have six meals per day or eat every 3 hours or something like that.
Here’s why this was a popular idea for a brief period of time:
Your body burns calories when it’s processing food. So the thought behind the more meals strategy was that if you ate more frequently, you would also burn more calories throughout the day. Thus, eating more meals should help you lose weight.
Here’s the problem:
The amount of calories you burn is proportional to the size of the meal your body is processing. So, digesting six smaller meals that add up to 2000 calories burns the same amount of energy as processing two large meals of 1000 calories each.
It doesn’t matter if you get your calories in 10 meals or in 1 meal, you’ll end up in the same place.
This is crazy. If I didn’t eat for 24 hours, I’d die.
Honestly, I think the mental barrier is the biggest thing that prevents people from fasting because it’s really not that hard to do in practice.
Here are a few reasons why intermittent fasting isn’t as crazy as you think it is.
First, fasting has been practiced by various religious groups for centuries. Medical practitioners have also noted the health benefits of fasting for thousands of years. In other words, fasting isn’t some new fad or crazy marketing ploy. It’s been around for a long time and it actually works.
Second, fasting seems foreign to many of us simply because nobody talks about it that much. The reason for this is that nobody stands to make much money by telling you to not eat their products, not take their supplements, or not buy their goods. In other words, fasting isn’t a very marketable topic and so you’re not exposed to advertising and marketing on it very often. The result is that it seems somewhat extreme or strange, even though its really not.
Third, you’ve probably already fasted many times, even though you don’t know it. Have you ever slept in late on the weekends and then had a late brunch? Some people do this every weekend. In situations like these, we often eat dinner the night before and then don’t eat until 11am or noon or even later. There’s your 16–hour fast and you didn’t even think about it.
Finally, I would suggest doing one 24–hour fast even if you don’t plan on doing intermittent fasting frequently. It’s good to teach yourself that you’ll survive just fine without food for a day. Plus, as I’ve outlined with multiple research studies throughout this article, there are a lot of health benefits of fasting.
What are some good resources on intermittent fasting?
You can learn a lot about intermittent fasting by reading articles like this one and the resources below, but the best way to learn about what actually works for you is to experiment. That said, I’d recommend the following resources.
Martin Berkhan’s site on the Leangains version of intermittent fasting is great. You can find it here. If you’re looking for a few articles to start with, I’d recommend this one, this one, and this one.
Andy Morgan has also created an excellent site that covers the Leangains model of intermittent fasting, which you can find here. I particularly like his method of counting macros instead of counting calories, which you can read about here. (That said, I don’t count anything. I just eat.)
There is a very active forum on Reddit where people post their own progress with the Leangains style of intermittent fasting. You can check that out here.
Brad Pilon wrote a good book on intermittent fasting called Eat Stop Eat, which you can buy here.
And finally, John Berardi’s report on intermittent fasting is a great example of testing the ideas in practice. You can .
That’s intermittent fasting in a nutshell.
Free Bonus: I created an Intermittent Fasting Quick Start Guide with a summary of the benefits of intermittent fasting and 3 fasting schedules you can use depending on your goals. It’s a quick 5 page PDF you can save and reference later as you try this yourself. .
Let’s be honest: The word “fasting” doesn’t exactly bring up delicious thoughts and positive vibes. For plenty of people, it probably conjures up images of starvation and deprivation and makes their stomach start growling.
Yet, intermittent fasting has so many folks going wild right now, raving about how the strict-and-scheduled eating plans helped them lose weight and improve their health. So there must be *some* good in the health and weight-loss fad, right?
Charlie Seltzer, MD, weight-loss physician and certified personal trainer, points out that what most people are doing nowadays isn’t “true” fasting (in other words, eating only one meal per day or nothing at all in a day’s period). Instead, they’re intermittent fasting (duh), meaning they’re taking an approach to eating that involves restricting calorie consumption to a certain window of time each day, like only from 11 a.m. to 7 p.m. (so you fast for 16 hours, a.k.a. a 16:8 diet).
The logic behind periodic fasting as a weight-loss approach: “Since you need to have a calorie deficit to lose weight, eating within a window makes it easier to eat less and hit your designated calories,” Dr. Seltzer explains.
Intermittent fasting has some pros beyond weight loss, too, says Dr. Seltzer. It works with a lot of people’s lifestyles, allowing them to skip meals during the day when they’re busy or not super hungry and might otherwise just eat out of obligation. What’s more, following a 5:2 fasting schedule may even improve your heart health; fasting can lower blood pressure and bad cholesterol, according to Cleveland HeartLab.
“True fasting has a large variety of health benefits beyond those that occur with calorie restriction,” Dr. Seltzer adds. “It can cause something called cellular autophagy, where our cells eat themselves .”
That said, intermittent fasting shouldn’t be attempted without some thought as to whether it’s really a good idea for your personality and lifestyle—and not just because it could be challenging to stick to, but because it could be downright bad for some groups of people.
Registered dietitian Barbie Boules of Barbie Boules Longevity Nutrition says the people who should not consider intermittent fasting are:
- Folks with diabetes or other metabolic disorders
- People taking medications that require food
- Anyone with a history of disordered eating
- Women who are pregnant or trying to conceive
- Children and teenagers
But honestly, anyone who requires a consistent, healthy input of calories throughout the day to be healthy (physically *and* emotionally!) isn’t the ideal candidate to try intermittent fasting. If you’re unsure where you stand, it’s always wise to speak with a medical professional first.
Here are eight potential disadvantages, side effects, and straight-up warnings about intermittent fasting to keep in mind if you’re a healthy adult and thinking about trying it yourself.
1. You might feel way hungrier.
Surprise, surprise: Not eating for 16 hours a day could make you ravenously hungry, at least while you’re in an adjustment period.
In theory, says Dr. Seltzer, intense hunger shouldn’t happen while intermittent fasting using a plan such as the 16:8 method; if you’re fasting correctly by filling up on protein at the end of the day, you shouldn’t be hungry first thing in the morning. (Your appetite wouldn’t kick in until later on the following day.)
In reality, though, this might take some getting used to. “The main worry is setting off binge-eating behavior, because you are so hungry you’re eating 5,000 calories ,” Dr. Seltzer explains.
In other words, only eating within a short window is not a free pass to set up camp at the all-you-can-eat buffet for eight hours, which would defeat the purpose of fasting. And this can be a huge challenge for many people who are used to eating much more regularly and who may not be totally in tune with their body’s hunger cues.
2. It might make you feel sick or fatigued in the morning, especially if you work out first thing.
Committed to your 6 a.m. workout? Intermittent fasting might not be a great choice. “I think it’s a terrible idea to exercise on an empty stomach,” says Boules. “We benefit from a little glucose before and some protein after.”
If you’re interested in experimenting with fasting periods and workout a ton, consider talking to a sports nutritionist or MD to assess your workout schedule and level of rigor. You might be okay fasting for a specific amount of time on days you don’t exercise, for instance. But if you’re, say, training for an endurance event, fueling your body around the clock and getting substantial calories is going to be much more important than trying to force fasting into your routine when your body is already being taxed by your training.
And even if you’re not a morning exerciser, not eating until, say, noon when you’re used to waking up and having breakfast at 8 a.m. may leave your stomach churning. In turn, you may feel off, a little lightheaded, or nauseous as you get used to the new schedule.
3. Fasting diets are rigid and rule-based.
Both Dr. Seltzer and Boules describe intermittent fasting as very individualized, meaning it could work well for some people and turn into a total disaster for others depending on a number of lifestyle factors.
Boules says that people who “like rules” might respond to the diet’s restrictive calorie window. But for others—like people who travel five days a week, changing time zones or schedules frequently—the diet will bring more stress than weight loss or other potential health perks. If the idea of watching the clock for permission to eat sounds unappealing to you, sit this one out.
4. It doesn’t always play nice with other diets.
Boules says intermittent fasting is often combined with other restrictive diets, like keto, which can cause double-trouble if either of those approaches—or heaven forbid both—aren’t right for you.
Adopting a diet plan that means you can only eat lean protein and vegetables between the hours of 1 and 9 p.m. every day doesn’t exactly set you up for winning any popularity contests with your friends and family (not to mention the mental fatigue that comes with jumping through meal-planning hoops on the regular), Boules points out.
But hey, your diet choices are your own, and if you are up for the challenge of navigating an intense and strict food routine and your personal life, that’s entirely your decision.
5. You may deal with low blood sugar.
This is why people with diabetes should steer clear of fasting. Low blood sugar, or hypoglycemia is a side effect of diabetes and insulin medication, but it can happen to non-diabetics, too (if you have thyroid disease, for example).
Not eating enough and skipping meals are common triggers for hypoglycemia. So, “people prone to hypoglycemia might feel dizzy or have nausea or shaking,” warns Dr. Seltzer.
Other symptoms of mild to moderate hypoglycemia include headache, blurred vision, sweating, fatigue, and paleness, according to the National Institute of Diabetes and Digestive and Kidney Diseases.
6. The research is minimal.
Look, we all know the internet is full of so-called health claims made by “experts” about the best diets. And while the field of research on intermittent fasting isn’t empty, Boules is hesitant to jump on the bandwagon based on what she’s seen so far.
“Despite a deluge of articles citing studies, solid evidence in support of intermittent fasting as a superior approach to eating just isn’t there yet,” she says.
What studies is Boules referring to? Well, most of the more compelling ones were actually performed on rodents. Human studies have not shown the same scope of evidence.
Want to know more about keto?
A few examples: A 2018 study published in Nutrition and Healthy Aging showed weight-loss results after 12 weeks of 16:8 intermittent fasting—but the sample size was only 23 people. A 2017 study in JAMA Internal Medicine showed that a fasting group of 100 participants lost more weight over a 12-month period than a non-dieting group, but not more than a group that cut calories overall.
There also remains debate about whether the actual fasting is responsible for the health benefits, or if it’s simply the reduction in calories.
This isn’t to say that better, more conclusive research won’t ever become available, but as Boules said, we’ve got a ways to go before we understand everything about intermittent fasting.
7. It doesn’t help you create mindful eating habits.
While Boules admits that intermittent fasting can be a great strategy for curbing mindless late-night snacking, it can totally work against mindful eating, too. Rather than thinking about whether or not you’re truly hungry, you’re simply eating by the clock.
“I encourage my clients to on a daily basis and act accordingly,” she says. “Every day is different for sleep, exercise, stress, hormones, and schedule, which all affects appetite. It’s one of many reasons I don’t believe it’s healthy to apply ‘rules’ to your food philosophy.”
8. You can take it too far.
Even in dieting, moderation is key; no diet is sustainable if you’re unable to adapt it to your lifestyle as needed. For example, Dr. Seltzer reiterates that many athletes need a morning meal and see better results when they eat before training. Sticking to a strict intermittent fasting schedule in that example precludes that.
Boules agrees: “I people not consuming anything but water prior to a challenging morning workout and for several hours after—this is simply not a good idea.”
Ultimately, if you’re just not sure how to feel about intermittent fasting, don’t hesitate to hash it out with a pro, like an RD or doc you trust.
At the end of the day, if you’re a healthy adult, intermittent fasting probably won’t do damage (even if it turns out to not be a good fit for you personally). Dr. Seltzer and Boules both acknowledge the control it teaches, though they remain on the fence about whether the potential side effects outweigh the benefits.
“Please understand this will not work for everyone and is not required for good health,” Boules says. “While I’m watching the research and will own it if I’m proven wrong, I think it’s yet another example of a fad approach to wellness.”
Sarah Bradley Sarah Bradley is a freelancer writer from Connecticut, where she lives with her husband and three sons.